Hydrogen-Mediated Electron Doping of Gold Clusters As Revealed by In Situ X-ray and UV-vis Absorption Spectroscopy.

PubMed

Ishida, Ryo; Hayashi, Shun; Yamazoe, Seiji; Kato, Kazuo; Tsukuda, Tatsuya

2017-06-01

We previously reported that small (∼1.2 nm) gold clusters stabilized by poly(N-vinyl-2-pyrrolidone) (Au:PVP) exhibited a localized surface plasmon resonance (LSPR) band at ∼520 nm in the presence of NaBH 4 . To reveal the mechanism of this phenomenon, the electronic structure of Au:PVP during the reaction with NaBH 4 in air was examined by means of in situ X-ray absorption spectroscopy at Au L 3 -edge and UV-vis spectroscopy. These measurements indicated that the appearance of the LSPR band is not associated with the growth in size but is ascribed to electron doping to the Au sp band by the adsorbed H atoms.

Detailed abundances for a large sample of giant stars in the globular cluster 47 Tucanae (NGC 104)

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

Cordero, M. J.; Pilachowski, C. A.; Johnson, C. I.

2014-01-01

47 Tuc is an ideal target to study chemical evolution and globular cluster (GC) formation in massive more metal-rich GCs, as it is the closest massive GC. We present chemical abundances for O, Na, Al, Si, Ca, Ti, Fe, Ni, La, and Eu in 164 red giant branch stars in the massive GC 47 Tuc using spectra obtained with both the Hydra multifiber spectrograph at the Blanco 4 m telescope and the FLAMES multiobject spectrograph at the Very Large Telescope. We find an average [Fe/H] = –0.79 ± 0.09 dex, consistent with literature values, as well as overabundances of alpha-elementsmore » ([α/Fe] ∼ 0.3 dex). The n-capture process elements indicate that 47 Tuc is r process-dominated ([Eu/La] = +0.24), and the light elements O, Na, and Al exhibit star-to-star variations. The Na-O anticorrelation, a signature typically seen in Galactic GCs, is present in 47 Tuc, and extends to include a small number of stars with [O/Fe] ∼ –0.5. Additionally, the [O/Na] ratios of our sample reveal that the cluster stars can be separated into three distinct populations. A Kolmogorov-Smirnov test demonstrates that the O-poor/Na-rich stars are more centrally concentrated than the O-rich/Na-poor stars. The observed number and radial distribution of 47 Tuc's stellar populations, as distinguished by their light element composition, agrees closely with the results obtained from photometric data. We do not find evidence supporting a strong Na-Al correlation in 47 Tuc, which is consistent with current models of asymptotic giant branch nucleosynthesis yields.« less

Flower-like Na2O nanotip synthesis via femtosecond laser ablation of glass

PubMed Central

2012-01-01

The current state-of-the-art in nanotip synthesis relies on techniques that utilize elaborate precursor chemicals, catalysts, or vacuum conditions, and any combination thereof. To realize their ultimate potential, synthesized nanotips require simpler fabrication techniques that allow for control over their final nano-morphology. We present a unique, dry, catalyst-free, and ambient condition method for creating densely clustered, flower-like, sodium oxide (Na2O) nanotips with controllable tip widths. Femtosecond laser ablation of a soda-lime glass substrate at a megahertz repetition rate, with nitrogen flow, was employed to generate nanotips with base and head widths as small as 100 and 20 nm respectively, and lengths as long as 10 μm. Control of the nanotip widths was demonstrated via laser dwell time with longer dwell times producing denser clusters of thinner nanotips. Energy dispersive X-ray analysis reveals that nanotip composition is Na2O. A new formation mechanism is proposed, involving an electrostatic effect between ionized nitrogen and polar Na2O. The synthesized nanotips may potentially be used in antibacterial and hydrogen storage applications. PMID:22809176

Probing electronic wave functions of sodium-doped clusters: Dyson orbitals, anisotropy parameters, and ionization cross-sections

DOE PAGES

Gunina, Anastasia O.; Krylov, Anna I.

2016-11-14

We apply high-level ab initio methods to describe the electronic structure of small clusters of ammonia and dimethylether (DME) doped with sodium, which provide a model for solvated electrons. We investigate the effect of the solvent and cluster size on the electronic states. We consider both energies and properties, with a focus on the shape of the electronic wave function and the related experimental observables such as photoelectron angular distributions. The central quantity in modeling photoionization experiments is the Dyson orbital, which describes the difference between the initial N-electron and final (N-1)-electron states of a system. Dyson orbitals enter themore » expression of the photoelectron matrix element, which determines total and partial photoionization cross-sections. We compute Dyson orbitals for the Na(NH3)n and Na(DME)m clusters using correlated wave functions (obtained with equation-of-motion coupled-cluster model for electron attachment with single and double substitutions) and compare them with more approximate Hartree-Fock and Kohn-Sham orbitals. As a result, we also analyze the effect of correlation and basis sets on the shapes of Dyson orbitals and the experimental observables.« less

CHEMICAL ABUNDANCES IN A SAMPLE OF RED GIANTS IN THE OPEN CLUSTER NGC 2420 FROM APOGEE

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

Souto, Diogo; Cunha, K.; Smith, V.

NGC 2420 is a ∼2 Gyr old well-populated open cluster that lies about 2 kpc beyond the solar circle, in the general direction of the Galactic anti-center. Most previous abundance studies have found this cluster to be mildly metal-poor, but with a large scatter in the obtained metallicities. Detailed chemical abundance distributions are derived for 12 red-giant members of NGC 2420 via a manual abundance analysis of high-resolution ( R = 22,500) near-infrared ( λ 1.5–1.7 μ m) spectra obtained from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. The sample analyzed contains six stars that are identified asmore » members of the first-ascent red giant branch (RGB), as well as six members of the red clump (RC). We find small scatter in the star-to-star abundances in NGC 2420, with a mean cluster abundance of [Fe/H] = −0.16 ± 0.04 for the 12 red giants. The internal abundance dispersion for all elements (C, N, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Co and Ni) is also very small (∼0.03–0.06 dex), indicating a uniform cluster abundance distribution within the uncertainties. NGC 2420 is one of the clusters used to calibrate the APOGEE Stellar Parameter and Chemical Abundance Pipeline (ASPCAP). The results from this manual analysis compare well with ASPCAP abundances for most of the elements studied, although for Na, Al, and V there are more significant offsets. No evidence of extra-mixing at the RGB luminosity bump is found in the {sup 12}C and {sup 14}N abundances from the pre-luminosity-bump RGB stars in comparison to the post-He core-flash RC stars.« less

OXYGEN AND SODIUM ABUNDANCES IN M13 (NGC 6205) GIANTS: LINKING GLOBULAR CLUSTER FORMATION SCENARIOS, DEEP MIXING, AND POST-RGB EVOLUTION

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

Johnson, Christian I.; Pilachowski, Catherine A., E-mail: cijohnson@astro.ucla.edu, E-mail: catyp@astro.indiana.edu

We present O, Na, and Fe abundances, as well as radial velocities, for 113 red giant branch (RGB) and asymptotic giant branch (AGB) stars in the globular cluster M13. The abundances and velocities are based on spectra obtained with the WIYN-Hydra spectrograph, and the observations range in luminosity from the horizontal branch (HB) to RGB tip. The results are examined in the context of recent globular cluster formation scenarios. We find that M13 exhibits many key characteristics that suggest its formation and chemical enrichment are well described by current models. Some of these observations include the central concentration of O-poormore » stars, the notable decrease in [O/Fe] (but small increase in [Na/Fe]) with increasing luminosity that affects primarily the 'extreme' population, the small fraction of stars with halo-like composition, and the paucity of O-poor AGB stars. In agreement with recent work, we conclude that the most O-poor M13 giants are likely He-enriched and that most (all?) O-poor RGB stars evolve to become extreme HB and AGB-manque stars. In contrast, the 'primordial' and 'intermediate' population stars appear to experience standard HB and AGB evolution.« less

A cluster ion chemistry for the mesospheric sodium layer

NASA Technical Reports Server (NTRS)

Richter, E. S.; Sechrist, C. F., Jr.

1979-01-01

A cluster ion chemistry for sodium is developed which relates the Na(+) profile to the Na profile using reactions involving Na(+).N2, Na(+).CO2, and Na(+).H2O. Removal of sodium from the mesosphere is accomplished by the formation of higher order clusters of the form Na(+).(H2O)n which presumably precipitate to the lower atmosphere. This sink is most effective in the 80-85 km altitude range. The chemical equilibrium model is applied to experimental observations of the Na and Na(+) layers.

Experimental and theoretical study of the microsolvation of sodium atoms in methanol clusters: differences and similarities to sodium-water and sodium-ammonia.

PubMed

Dauster, Ingo; Suhm, Martin A; Buck, Udo; Zeuch, Thomas

2008-01-07

Methanol clusters are generated in a continuous He-seeded supersonic expansion and doped with sodium atoms in a pick-up cell. By this method, clusters of the type Na(CH(3)OH)(n) are formed and subsequently photoionized by applying a tunable dye-laser system. The microsolvation process of the Na 3s electron is studied by determining the ionization potentials (IPs) of these clusters size-selectively for n = 2-40. A decrease is found from n = 2 to 6 and a constant value of 3.19 +/- 0.07 eV for n = 6-40. The experimentally-determined ionization potentials are compared with ionization potentials derived from quantum-chemical calculations, assuming limiting vertical and adiabatic processes. In the first case, energy differences are calculated between the neutral and the ionized cationic clusters of the same geometry. In the second case, the ionized clusters are used in their optimized relaxed geometry. These energy differences and relative stabilities of isomeric clusters vary significantly with the applied quantum-chemical method (B3LYP or MP2). The comparison with the experiment for n = 2-7 reveals strong variations of the ionization potential with the cluster structure indicating that structural diversity and non-vertical pathways give significant signal contributions at the threshold. Based on these findings, a possible explanation for the remarkable difference in IP evolutions of methanol or water and ammonia is presented: for methanol and water a rather localized surface or semi-internal Na 3s electron is excited to either high Rydberg or more localized states below the vertical ionization threshold. This excitation is followed by a local structural relaxation that couples to an autoionization process. For small clusters with n < 6 for methanol and n < 4 for water the addition of solvent molecules leads to larger solvent-metal-ion interaction energies, which consequently lead to lower ionization thresholds. For n = 6 (methanol) and n = 4 (water) this effect comes to a halt, which may be connected with the completion of the first cationic solvation shell limiting the release of local relaxation energy. For Na(NH(3))(n), a largely delocalized and internal electron is excited to autoionizing electronic states, a process that is no longer local and consequently may depend on cluster size up to very large n.

Distribution of cardiac sodium channels in clusters potentiates ephaptic interactions in the intercalated disc.

PubMed

Hichri, Echrak; Abriel, Hugues; Kucera, Jan P

2018-02-15

It has been proposed that ephaptic conduction, relying on interactions between the sodium (Na + ) current and the extracellular potential in intercalated discs, might contribute to cardiac conduction when gap junctional coupling is reduced, but this mechanism is still controversial. In intercalated discs, Na + channels form clusters near gap junction plaques, but the functional significance of these clusters has never been evaluated. In HEK cells expressing cardiac Na + channels, we show that restricting the extracellular space modulates the Na + current, as predicted by corresponding simulations accounting for ephaptic effects. In a high-resolution model of the intercalated disc, clusters of Na + channels that face each other across the intercellular cleft facilitate ephaptic impulse transmission when gap junctional coupling is reduced. Thus, our simulations reveal a functional role for the clustering of Na + channels in intercalated discs, and suggest that rearrangement of these clusters in disease may influence cardiac conduction. It has been proposed that ephaptic interactions in intercalated discs, mediated by extracellular potentials, contribute to cardiac impulse propagation when gap junctional coupling is reduced. However, experiments demonstrating ephaptic effects on the cardiac Na + current (I Na ) are scarce. Furthermore, Na + channels form clusters around gap junction plaques, but the electrophysiological significance of these clusters has never been investigated. In patch clamp experiments with HEK cells stably expressing human Na v 1.5 channels, we examined how restricting the extracellular space modulates I Na elicited by an activation protocol. In parallel, we developed a high-resolution computer model of the intercalated disc to investigate how the distribution of Na + channels influences ephaptic interactions. Approaching the HEK cells to a non-conducting obstacle always increased peak I Na at step potentials near the threshold of I Na activation and decreased peak I Na at step potentials far above threshold (7 cells, P = 0.0156, Wilcoxon signed rank test). These effects were consistent with corresponding control simulations with a uniform Na + channel distribution. In the intercalated disc computer model, redistributing the Na + channels into a central cluster of the disc potentiated ephaptic effects. Moreover, ephaptic impulse transmission from one cell to another was facilitated by clusters of Na + channels facing each other across the intercellular cleft when gap junctional coupling was reduced. In conclusion, our proof-of-principle experiments demonstrate that confining the extracellular space modulates cardiac I Na , and our simulations reveal the functional role of the aggregation of Na + channels in the perinexus. These findings highlight novel concepts in the physiology of cardiac excitation. © 2017 The Authors. The Journal of Physiology © 2017 The Physiological Society.

Multiple populations in more metal-rich galactic globular clusters

NASA Astrophysics Data System (ADS)

Cordero, Maria J.

In this thesis we present chemical abundances for bright stars in the intermediate metallicity globular cluster (GC) M5, and the relatively metal-rich GCs M71 and 47 Tuc with the goal of improving the understanding of chemical evolution in the metallicity regime sampled by these three GCs. The first chapter presents a brief historical overview in light element abundance variations in globular clusters. In the second chapter we present the results obtained for 47 Tuc, the most-metal rich cluster of my sample. 47 Tuc is an ideal target to study chemical evolution and GC formation in massive more metal-rich GCs since it is the closest massive GC. Chemical abundances for O, Na, Al, Si, Ca, Ti, Fe, Ni, La, and Eu were determined for 164 red giant branch (RGB) stars in 47 Tuc using spectra obtained with both the Hydra multi-fiber spectrograph at the Blanco 4-m telescope and the FLAMES multi-object spectrograph at the ESO Very Large Telescope. The average [Fe/H]= --0.79+/-0.09 dex is consistent with literature values, as well as over-abundances of alpha-elements ([alpha/Fe] ~ 0.3 dex). The n-capture process elements indicate that 47 Tuc is r-process dominated ([Eu/La]=+0.24), and the light elements O, Na, and Al exhibit star-to-star variations. The Na-O anti-correlation, a signature typically seen in Galactic GCs, is present in 47 Tuc, and extends to include a small number of stars with [O/Fe] ~ --0.5. Additionally, the [O/Na] ratios of our sample reveal that the cluster stars can be separated into three distinct populations. A KS-test demonstrates that the O-poor/Na-rich stars are more centrally concentrated than the O-rich/Na-poor stars. The observed number and radial distribution of 47 Tuc's stellar populations, as distinguished by their light element composition, agrees closely with the results obtained from photometric data. We do not find evidence supporting a strong Na-Al correlation in 47 Tuc, which is consistent with current models of AGB nucleosynthesis yields. Aluminum is the heaviest light element displaying large star-to-star variations in Galactic GCs. This element may provide additional insight into the origin of the multiple populations and the nature of the first-generation stars responsible for chemical inhomogeneities. We found that, unlike more metal-poor GCs, 47 Tuc did not exhibit a strong Na-Al correlation, which motivates a careful study of the similar metallicity but less massive GC M71. In chapter 3, we present chemical abundances of O, Na, Al, and Fe for 33 giants in M71 using spectra obtained with the WIYN-Hydra spectrograph. Our spectroscopic analysis finds that, similar to 47 Tuc and in contrast with more metal-poor GCs, M71 stars do not exhibit a strong Na-Al correlation and span a relatively narrow range in [Al/Fe]. Furthermore, these data suggest that only a small fraction of stars (29%) have an [Na/Fe] ratio similar to halo stars at this metallicity, which is a characteristic reproduced by GC formation and evolution models. In the fourth chapter we present chemical abundances for a sample of 61 red giants in the intermediate-metallicity GC M5. The data were obtained using the Hydra multi-fiber positioner and bench spectrograph on the WIYN telescope. We find that our abundance ratios for Na, Al, Si, Ca, Ti, Fe, Ni, La, and Eu agree with published values for this cluster. The scatter seen in Fe-peak, alpha, and neutron-capture elements is consistent with typical spectroscopic errors. However, we identified a star modestly enhanced in La by performing a careful comparison of stellar spectra with similar atmospheric parameters. La-enhanced stars are rare in GCs. For instance, we have found only one such star in each of M5 and 47 Tuc. M5 red giants exhibit a strong Na-Al correlation, which is absent in M71 and 47 Tuc. Furthermore, M5 is at the metallicity regime where GCs seem to transition from small to large [Al/Fe] scatter. Interestingly, this metallicity regime also separates metal-poor from metal-rich Galactic GCs. In the fifth chapter we present radial distributions, population fractions, detailed examination of behavior of Al in more metal-rich GCs in the context of cluster chemical evolution, and, finally, a kinematical study of the GC M13 using spectra acquired with the WIYN-Hydra spectrograph. We find a rotational signal and a kinematical difference between the intermediate and extreme generations. Specifically, we find that the extreme O-depleted population, which is also more centrally concentrated than the primordial and intermediate populations, has the highest rotational amplitude. (Abstract shortened by UMI.)

Adsorption of Bromine on Gold Nanoclusters

NASA Astrophysics Data System (ADS)

Salvo, Christopher; Keagy, Josiah; Yarmoff, Jory

Small metal nanoclusters are extremely effective as catalysts, with rates that rival those of enzymes in biological systems. The first step in a catalytic reaction is the adsorption of a precursor molecule. The neutralization of alkali projectiles during low energy ion scattering (LEIS), which is acutely sensitive to the local electrostatic potential a few Å's above the surface, is used here to probe Au nanoclusters grown on SiO2 as they are reacted with Br2. Previous work had demonstrated very efficient neutralization in scattering from small catalytically active Au clusters, which was interpreted as an indication that the bare clusters are negatively charged. X-ray photoelectron spectroscopy and LEIS show little or no Br signal after exposing SiO2 and Au foil to Br2, suggesting that adsorption does not occur because the Br-Br bond does not break. Dissociative adsorption occurs rapidly, however, when small Au nanoclusters are reacted with Br2. 1.5 keV Na+ ions scattered from the Au clusters show a decrease in the neutralization probability as Br is reacted, indicating that adsorption results in charge being transferred from the cluster to the Br adatom. This material is based upon work supported by the National Science Foundation under CHE - 1611563.

Insight from first principles into the stability and magnetism of alkali-metal superoxide nanoclusters

NASA Astrophysics Data System (ADS)

Arcelus, Oier; Suaud, Nicolas; Katcho, Nebil A.; Carrasco, Javier

2017-05-01

Alkali-metal superoxides are gaining increasing interest as 2p magnetic materials for information and energy storage. Despite significant research efforts on bulk materials, gaps in our knowledge of the electronic and magnetic properties at the nanoscale still remain. Here, we focused on the role that structural details play in determining stability, electronic structure, and magnetic couplings of (MO2)n (M = Li, Na, and K, with n = 2-8) clusters. Using first-principles density functional theory based on the Perdew-Burke-Ernzerhof and Heyd-Scuseria-Ernzerhof functionals, we examined the effect of atomic structure on the relative stability of different polymorphs within each investigated cluster size. We found that small clusters prefer to form planar-ring structures, whereas non-planar geometries become more stable when increasing the cluster size. However, the crossover point depends on the nature of the alkali metal. Our analysis revealed that electrostatic interactions govern the highly ionic M-O2 bonding and ultimately control the relative stability between 2-D and 3-D geometries. In addition, we analyzed the weak magnetic couplings between superoxide molecules in (NaO2)4 clusters comparing model Hamiltonian methods based on Wannier function projections onto πg states with wave function-based multi-reference calculations.

Cyanide leaching of Au/CeO2: highly active gold clusters for 1,3-butadiene hydrogenation.

PubMed

Guan, Y; Hensen, E J M

2009-11-07

Ceria-supported gold catalysts before and after leaching by NaCN were investigated by X-ray absorption spectroscopy at the Au L(III) edge. After gold leaching, isolated gold cations remain in close interaction with the support. These ions form an ideal precursor to very small clusters of a few gold atoms upon reduction. The resulting gold clusters exhibit a very high intrinsic activity in the hydrogenation of 1,3-butadiene, which is at least one order of magnitude higher than that of the nanometre-sized gold particles in the non-leached parent catalyst. These findings point to a very strong structure sensitivity of the gold-catalyzed hydrogenation of dienes.

Studying the Effect of a Composition of the Cluster Core in High-Radiopacity Cluster Complexes of Rhenium on Their Acute Toxicity In Vivo.

PubMed

Pozmogova, T N; Krasil'nikova, A A; Ivanov, A A; Shestopalov, M A; Gyrylova, S N; Shestopalova, L V; Shestopaloiv, A M; Shkurupy, V A

2016-05-01

An in vivo study was performed to evaluate the dependence of acute toxicity of high-radiopacity and luminescent octahedral cluster complexes of rhenium after intravenous injection on a composition of the cluster core. Changes in mouse body weight, water and food consumption, degree of intoxication, and morphological changes in the visceral organs were studied after intravenous injection of the following cluster complexes with various internal ligands (S, Se, or Te): Na4[{Re 6 Te 8 }(CN)6], Na4[{Re 6 Se 8 }(CN)6], and Na4[{Re 6 S 8 }(CN)6]. The Na4[{Re 6 S 8 } (CN)6] cluster complex was shown to be the safest for animals.

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

PubMed

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

2012-09-27

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

Influence of halogenides on luminescence from silver molecular clusters in photothermorefractive glasses

NASA Astrophysics Data System (ADS)

Dubrovin, V. D.; Ignat'ev, A. I.; Nikonorov, N. V.; Sidorov, A. I.

2014-05-01

It is shown experimentally that a rise in the sodium halogenide (NaCl, NaBr) concentration in photothermorefractive glasses increases the intensity of luminescence from silver neutral molecular clusters. Substitution of NaBr for NaCl with their concentration being the same shifts the luminescence band toward longer waves and raises its intensity. These findings can be explained by the formation of molecular clusters of type Ag n -Hal (Hal = Cl, Br) in photothermorefractive glass.

Geometric and electronic structures of silicon-sodium binary clusters. I. Ionization energy of SinNam

NASA Astrophysics Data System (ADS)

Kishi, Reiko; Iwata, Suehiro; Nakajima, Atsushi; Kaya, Koji

1997-08-01

Sodium doped silicon clusters (SinNam; 1⩽n⩽14, 1⩽m⩽5) produced by two types of laser vaporization were studied. The adsorption of Na atoms on the Sin clusters leads the substantial lowering of the ionization energy, Ei, of SinNam clusters. Their reactivity toward NO molecules was measured with a fast flow reactor, and the anticorrelation between the Eis and the reactivity was clearly observed; species having low Ei exhibit high reactivity and vice versa. Moreover, the clear parallelism between the Eis of SinNa and the EAs of Sin is found. This is consistent with the fact that the structure of SinNa clusters keeps the frame of the corresponding Sin cluster unchanged and that the electronic structure of SinNa is similar to that of the corresponding negative ion Sin-. In addition to the experimental studies, the geometries, adsorption energies, and vertical ionization energies of SinNa (n=1-7) were investigated with ab initio MO calculations including electron correlation; The Møller-Plesset perturbation theory was used and the configuration interaction (CI) calculation was carried out, particularly for a diatomic molecule, SiNa.

Time-resolved in situ XAS study of the preparation of supported gold clusters.

PubMed

Bus, Eveline; Prins, Roel; van Bokhoven, Jeroen A

2007-07-07

Incipient-wetness impregnation of gamma-Al(2)O(3) with HAuCl(4) and subsequent removal of chlorine with NaOH, and deposition-precipitation of HAuCl(4) on TiO(2) at pH 7 resulted in supported Au(3+) species. Time-resolved in situ XAS at the Au L(3) edge showed that the Al(2)O(3)-supported oxidic or hydroxidic species were reduced in hydrogen at 440 K to yield small metallic gold clusters. The Au(3+) precursor decomposed to metallic gold in inert atmosphere at 573 K and in oxidizing atmosphere above 623 K. In all atmospheres, initially small clusters were formed that gradually grew with increasing temperature. The TiO(2)-supported species were considerably less stable. In hydrogen and carbon monoxide, Au(0) clusters of 1 to 1.5 nm were formed at room temperature, which was the lowest temperature studied. In inert and oxidizing atmosphere, the Au(3+) precursor decomposed fully to metallic gold at 530 K, as shown by XAS and temperature-programmed experiments. Large clusters were obtained already in the initial stage of reduction. Residual chlorine inhibited the reduction and led to sintering of the gold clusters. Exposure of the TiO(2)-supported catalyst precursor to light or the X-ray beam led to partial reduction, and STEM showed that storage of the reduced gold clusters under ambient conditions led to agglomeration and bimodal cluster-size distributions.

Effects of levomilnacipran ER on noradrenergic symptoms, anxiety symptoms, and functional impairment in adults with major depressive disorder: Post hoc analysis of 5 clinical trials.

PubMed

Blier, Pierre; Gommoll, Carl; Chen, Changzheng; Kramer, Kenneth

2017-03-01

To evaluate the effects of levomilnacipran extended-release (LVM-ER; 40-120mg/day) on noradrenergic (NA) and anxiety-related symptoms in adults with major depressive disorder (MDD) and explore the relationship between these symptoms and functional impairment. Data were pooled from 5 randomized, double-blind, placebo-controlled trials (N=2598). Anxiety and NA Cluster scores were developed by adding selected item scores from the Montgomery-Åsberg Depression Rating Scale (MADRS) and 17-item Hamilton Depression Rating Scale (HAMD 17 ). A path analysis was conducted to estimate the direct effects of LVM-ER on functional impairment (Sheehan Disability Scale [SDS] total score) and the indirect effects through changes in NA and Anxiety Cluster scores. Mean improvements from baseline in NA and Anxiety Cluster scores were significantly greater with LVM-ER versus placebo (both P<0.001), as were the response rates (≥50% score improvement): NA Cluster (44% vs 34%; odds ratio=1.56; P<0.0001); Anxiety Cluster (39% vs 36%; odds ratio=1.19; P=0.041). Mean improvement in SDS total score was also significantly greater with LVM-ER versus placebo (-7.3 vs -5.6; P<0.0001). LVM-ER had an indirect effect on change in SDS total score that was mediated more strongly through NA Cluster score change (86%) than Anxiety Cluster score change (18%); the direct effect was negligible. NA and Anxiety Cluster scores, developed based on the face validity of individual MADRS and HAMD 17 items, were not predefined as efficacy outcomes in any of the studies. In adults with MDD, LVM-ER indirectly improved functional impairment mainly through improvements in NA symptoms and less so via anxiety symptoms. Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.

Communication. Kinetics of scavenging of small, nucleating clusters. First nucleation theorem and sum rules

DOE PAGES

Malila, Jussi; McGraw, Robert; Laaksonen, Ari; ...

2015-01-07

Despite recent advances in monitoring nucleation from a vapor at close-to-molecular resolution, the identity of the critical cluster, forming the bottleneck for the nucleation process, remains elusive. During past twenty years, the first nucleation theorem has been often used to extract the size of the critical cluster from nucleation rate measurements. However, derivations of the first nucleation theorem invoke certain questionable assumptions that may fail, e.g., in the case of atmospheric new particle formation, including absence of subcritical cluster losses and heterogeneous nucleation on pre-existing nanoparticles. Here we extend the kinetic derivation of the first nucleation theorem to give amore » general framework to include such processes, yielding sum rules connecting the size dependent particle formation and loss rates to the corresponding loss-free nucleation rate and the apparent critical size from a naïve application of the first nucleation theorem that neglects them.« less

Depth of focus extended microscope configuration for imaging of incorporated groups of molecules, DNA constructs and clusters inside bacterial cells

NASA Astrophysics Data System (ADS)

Fessl, Tomas; Ben-Yaish, Shai; Vacha, Frantisek; Adamec, Frantisek; Zalevsky, Zeev

2009-07-01

Imaging of small objects such as single molecules, DNA clusters and single bacterial cells is problematic not only due to the lateral resolution that is obtainable in currently existing microscopy but also, and as much fundamentally limiting, due to the lack of sufficient axial depth of focus to have the full object focused simultaneously. Extension in depth of focus is helpful also for single molecule steady state FRET measurements. In this technique it is crucial to obtain data from many well focused molecules, which are often located in different axial depths. In this paper we present the implementation of an all-optical and a real time technique of extension in the depth of focus that may be incorporated in any high NA microscope system and to be used for the above mentioned applications. We demonstrate experimentally how after the integration of special optical element in high NA 100× objective lens of a single molecule imaging microscope system, the depth of focus is significantly improved while maintaining the same lateral resolution in imaging applications of incorporated groups of molecules, DNA constructs and clusters inside bacterial cells.

Aromatization of n-hexane by platinum-containing molecular sieves. 2. n-Hexane reactivity

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

Mielczarski, E.; Suk Bong Hong; Davis, M.E.

Pt/KL, Pt/BaKL, Pt/KBaKL, Pt/NaY, Pt/CsNaY, Pt/NaFAU(C), Pt/hex, Pt/SSZ-24, Pt/silica, and Pt/carbon were tested as catalysts for the aromatization of n-hexane at 460-510 C and atmospheric total pressure in order to study the influence of Pt cluster size and support acidity/basicity, microstructure, and chemical composition on activity and selectivity. Analysis of the catalytic and NH{sub 3} temperature-programmed desorption results from Pt/KL, Pt/BaKL, and Pt/KBaKL reveals that the presence of any acidity increases hydrogenolysis at the expense of benzene production. In addition, no increase in aromatization selectivity is observed by the addition of base sites to a Pt/zeolite catalyst, confirming that aromatizationmore » of n-hexane over Pt clusters on nonacidic carriers is monofunctional. High selectivity to benzene over most of the zeolite samples demonstrates that support microstructure does not contribute directly to the aromatization selectivity over Pt catalysts. High selectivity to benzene is observed for a Pt/carbon catalyst suggesting that a zeolitic support is not necessary for good performance. In fact, similar reactivity is obtained from microporous (Pt/SSZ-24) and nonmicroporous (Pt/silica) silica supported platinum catalysts with similar H/Pt values. A clear trend of increasing benzene selectivity with decreasing Pt cluster size is found. These observations suggest that the exceptional reactivity of Pt/KL for the aromatization of n-hexane results from the lack of any acidity in the support and the ability of zeolite L to stabilize the formation of extremely small Pt clusters.« less

First-principles study of amorphous carbon: a promising candidate for Na-ion batteries

NASA Astrophysics Data System (ADS)

Kotsis, Konstantinos; Legrain, Fleur; Manzhos, Sergei

2015-03-01

The perspective of a widespread use of clean but intermittent sources of electricity (wind and solar) as well as that of hybrid electric vehicles calls for alternatives to Li-ion batteries as Li resources are limited. Na being abundant, cheap, and a relatively light and small atom, Na-ion batteries have attracted a lot of interest the past few years. However, while most of the Na-ion batteries studies focus on the positive electrode, the negative electrode remains little investigated and an efficient anode providing all a good capacity, a high cycle life, and a descent rate of charge/discharge, is still not available. The efficient electrode materials for Li, in particular diamond Si and graphite C, have been shown to not allow the intercalation of Na [1, 2]. Computational studies report positive intercalation energies [3, 4] and therefore suggest that the insertion of Na into the crystalline framework (C and Si) is thermodynamically not favored: Na atoms prefer to gather into Na clusters rather than to intercalate into the crystalline phase. Amorphization of Si was found to be a valid strategy to improve the interaction between Si and Na [3]. We investigate here the effects of amorphization of C on its storage properties vis-à-vis Na (as well as Li for reference).

Energetics of charged metal clusters containing vacancies

NASA Astrophysics Data System (ADS)

Pogosov, Valentin V.; Reva, Vitalii I.

2018-01-01

We study theoretically large metal clusters containing vacancies. We propose an approach, which combines the Kohn-Sham results for monovacancy in a bulk of metal and analytical expansions in small parameters cv (relative concentration of vacancies) and RN,v -1, RN ,v being cluster radii. We obtain expressions of the ionization potential and electron affinity in the form of corrections to electron work function, which require only the characteristics of 3D defect-free metal. The Kohn-Sham method is used to calculate the electron profiles, ionization potential, electron affinity, electrical capacitance; dissociation, cohesion, and monovacancy-formation energies of the small perfect clusters NaN, MgN, AlN (N ≤ 270) and the clusters containing a monovacancy (N ≥ 12) in the stabilized-jellium model. The quantum-sized dependences for monovacancy-formation energies are calculated for the Schottky scenario and the "bubble blowing" scenario, and their asymptotic behavior is also determined. It is shown that the asymptotical behaviors of size dependences for these two mechanisms differ from each other and weakly depend on the number of atoms in the cluster. The contribution of monovacancy to energetics of charged clusters and the size dependences of their characteristics and asymptotics are discussed. It is shown that the difference between the characteristics for the neutral and charged clusters is entirely determined by size dependences of ionization potential and electron affinity. Obtained analytical dependences may be useful for the analysis of the results of photoionization experiments and for the estimation of the size dependences of the vacancy concentration including the vicinity of the melting point.

Correlation study of sodium-atom chemisorption on the GaAs(110) surface

NASA Astrophysics Data System (ADS)

Song, K. M.; Khan, D. C.; Ray, A. K.

1994-01-01

Different possible adsorption sites of sodium atoms on a gallium arsenide surface have been investigated using ab initio self-consistent unrestricted Hartree-Fock total-energy cluster calculations with Hay-Wadt effective core potentials. The effects of electron correlation have been included by invoking the concepts of many-body perturbation theory and are found to be highly significant. We find that the Na-atom adsorption at a site modeled with an NaGa5As4H12 cluster is most favored energetically followed by Na adsorption at the site modeled with the NaGa4As5H12 cluster. The effects of charge transfer from Na to the GaAs surface as also possibilities of metallization are also analyzed and discussed.

Surface characterization of tin-based inorganic EUV resists

NASA Astrophysics Data System (ADS)

Frederick, Ryan T.; Diulus, J. Trey; Lyubinetsky, Igor; Hutchison, Danielle C.; Olsen, Morgan R.; Nyman, May; Herman, Gregory S.

2018-03-01

Metal oxide nanomaterials have shown promise for use as EUV resists. Recently, significant efforts have focused on tinoxo clusters that have high absorption coefficient Sn centers and radiation sensitive organic ligands. In our studies, we have investigated a β-Keggin butyl-Sn cluster (β-NaSn13), which is charge-neutral and allows studying radiation induced chemistries without interference from counterions. We have used ambient pressure X-ray photoelectron spectroscopy (APXPS) to investigate the contrast properties of the β-NaSn13 in ultrahigh vacuum (UHV) and in the presence of ambient oxygen. These contrast studies indicate that ambient oxygen reduces the dose requirements for the solubility transition of the β-NaSn13 photoresists. APXPS spectra collected before and after the solubility transition shows that ambient oxygen causes a greater loss of butyl ligands from the samples and the formation of more tin oxide for larger doses, suggesting the presence of reactive oxygen species. APXPS was also used to study processes during the post exposure bake, where we compared the differences in film chemistries in ambient oxygen or in UHV. There were only very small differences in the APXPS spectra before exposure and after exposure and the post exposure bake. However, ambient oxygen resulted in some changes for unexposed regions during the post exposure bake; there was a greater ratio of tin oxide to other oxygen species (alkoxy ligands, hydroxyls) for samples annealed in oxygen. These results have significance for EUV and e-beam lithography processing parameters, as well as implications for cluster design and ligand chemistries.

Temperature-dependent solubility transition of Na₂SO₄ in water and the effect of NaCl therein: solution structures and salt water dynamics.

PubMed

Bharmoria, Pankaj; Gehlot, Praveen Singh; Gupta, Hariom; Kumar, Arvind

2014-11-06

Dual, aqueous solubility behavior of Na2SO4 as a function of temperatures is still a natural enigma lying unresolved in the literature. The solubility of Na2SO4 increases up to 32.38 °C and decreases slightly thereafter at higher temperatures. We have thrown light on this phenomenon by analyzing the Na2SO4-water clusters (growth and stability) detected from temperature-dependent dynamic light scattering experiments, solution compressibility changes derived from the density and speed of sound measurements, and water structural changes/Na2SO4 (ion pair)-water interactions observed from the FT-IR and 2D DOSY (1)H NMR spectroscopic investigations. It has been observed that Na2SO4-water clusters grow with an increase in Na2SO4 concentration (until the solubility transition temperature) and then start decreasing afterward. An unusual decrease in cluster size and solution compressibility has been observed with the rise in temperature for the Na2SO4 saturated solutions below the solubility transition temperature, whereas an inverse pattern is followed thereafter. DOSY experiments have indicated different types of water cluster species in saturated solutions at different temperatures with varying self-diffusion coefficients. The effect of NaCl (5-15 wt %) on the solubility behavior of Na2SO4 at different temperatures has also been examined. The studies are important from both fundamental and industrial application points of view, for example, toward the clean separation of NaCl and Na2SO4 from the effluent streams of textile and tannery industries.

Highly Efficient Differentiation and Enrichment of Spinal Motor Neurons Derived from Human and Monkey Embryonic Stem Cells

PubMed Central

Wada, Tamaki; Honda, Makoto; Minami, Itsunari; Tooi, Norie; Amagai, Yuji; Nakatsuji, Norio; Aiba, Kazuhiro

2009-01-01

Background There are no cures or efficacious treatments for severe motor neuron diseases. It is extremely difficult to obtain naïve spinal motor neurons (sMNs) from human tissues for research due to both technical and ethical reasons. Human embryonic stem cells (hESCs) are alternative sources. Several methods for MN differentiation have been reported. However, efficient production of naïve sMNs and culture cost were not taken into consideration in most of the methods. Methods/Principal Findings We aimed to establish protocols for efficient production and enrichment of sMNs derived from pluripotent stem cells. Nestin+ neural stem cell (NSC) clusters were induced by Noggin or a small molecule inhibitor of BMP signaling. After dissociation of NSC clusters, neurospheres were formed in a floating culture containing FGF2. The number of NSCs in neurospheres could be expanded more than 30-fold via several passages. More than 33% of HB9+ sMN progenitor cells were observed after differentiation of dissociated neurospheres by all-trans retinoic acid (ATRA) and a Shh agonist for another week on monolayer culture. HB9+ sMN progenitor cells were enriched by gradient centrifugation up to 80% purity. These HB9+ cells differentiated into electrophysiologically functional cells and formed synapses with myotubes during a few weeks after ATRA/SAG treatment. Conclusions and Significance The series of procedures we established here, namely neural induction, NSC expansion, sMN differentiation and sMN purification, can provide large quantities of naïve sMNs derived from human and monkey pluripotent stem cells. Using small molecule reagents, reduction of culture cost could be achieved. PMID:19701462

Characterization of a Large Cluster of Influenza A(H1N1)pdm09 Viruses Cross-Resistant to Oseltamivir and Peramivir during the 2013-2014 Influenza Season in Japan

PubMed Central

Takashita, Emi; Kiso, Maki; Fujisaki, Seiichiro; Yokoyama, Masaru; Nakamura, Kazuya; Shirakura, Masayuki; Sato, Hironori; Odagiri, Takato; Kawaoka, Yoshihiro

2015-01-01

Between September 2013 and July 2014, 2,482 influenza 2009 pandemic A(H1N1) [A(H1N1)pdm09] viruses were screened in Japan for the H275Y substitution in their neuraminidase (NA) protein, which confers cross-resistance to oseltamivir and peramivir. We found that a large cluster of the H275Y mutant virus was present prior to the main influenza season in Sapporo/Hokkaido, with the detection rate for this mutant virus reaching 29% in this area. Phylogenetic analysis suggested the clonal expansion of a single mutant virus in Sapporo/Hokkaido. To understand the reason for this large cluster, we examined the in vitro and in vivo properties of the mutant virus. We found that it grew well in cell culture, with growth comparable to that of the wild-type virus. The cluster virus also replicated well in the upper respiratory tract of ferrets and was transmitted efficiently between ferrets by way of respiratory droplets. Almost all recently circulating A(H1N1)pdm09 viruses, including the cluster virus, possessed two substitutions in NA, V241I and N369K, which are known to increase replication and transmission fitness. A structural analysis of NA predicted that a third substitution (N386K) in the NA of the cluster virus destabilized the mutant NA structure in the presence of the V241I and N369K substitutions. Our results suggest that the cluster virus retained viral fitness to spread among humans and, accordingly, caused the large cluster in Sapporo/Hokkaido. However, the mutant NA structure was less stable than that of the wild-type virus. Therefore, once the wild-type virus began to circulate in the community, the mutant virus could not compete and faded out. PMID:25691635

The Role of Structural and Compositional Heterogeneities in the Insulator-to-Metal Transition in Hole-Doped APd3O4 (A = Ca, Sr).

PubMed

Lamontagne, Leo K; Laurita, Geneva; Knight, Michael; Yusuf, Huma; Hu, Jerry; Seshadri, Ram; Page, Katharine

2017-05-01

The cubic semiconducting compounds APd 3 O 4 (A = Ca, Sr) can be hole-doped by Na substitution on the A site and driven toward more conducting states. This process has been followed here by a number of experimental techniques to understand the evolution of electronic properties. While an insulator-to-metal transition is observed in Ca 1-x Na x Pd 3 O 4 for x ≥ 0.15, bulk metallic behavior is not observed for Sr 1-x Na x Pd 3 O 4 up to x = 0.20. Given the very similar crystal and (calculated) electronic structures of the two materials, the distinct behavior is a matter of interest. We present evidence of local disorder in the A = Sr materials through the analysis of the neutron pair distribution function, which is potentially at the heart of the distinct behavior. Solid-state 23 Na nuclear magnetic resonance studies additionally suggest a percolative insulator-to-metal transition mechanism, wherein presumably small regions with a signal resembling metallic NaPd 3 O 4 form almost immediately upon Na substitution, and this signal grows monotonically with substitution. Some signatures of increased local disorder and a propensity for Na clustering are seen in the A = Sr compounds.

Correlation between cation conduction and ionic morphology in a PEO-based single ion conductor

NASA Astrophysics Data System (ADS)

Lin, Kan-Ju; Maranas, Janna

2011-03-01

We use molecular dynamics simulation to study ion transport and backbone mobility of a PEO-based single ion conductor. Ion mobility depends on the chemical structure and the local environment of the ions, which consequently impact ionic conductivity. We characterize the aggregation state of the ions, and assess the role of ion complexes in ionomer dynamics. In addition to solvated cations and pairs, higher order ion clusters are found. Most of the ion clusters are in string-like structure and cross-link two or more different ionomer chains through ionic binding. Ionic crosslinks decrease mobility at the ionic co-monomer; hence the mobility of the adjacent PEO segment is influenced. Na ions show slow mobility when they are inside large clusters. The hopping timescale for Na varies from 20 ns to 200. A correlation is found between Na mobility and the number of hops from one coordination site to another. Besides ether oxygens, Na ions in the ionomer also use the anion and the edge of the cluster as hopping sites. The string-like structure of clusters provide less stable sites at the two ends thus ions are more mobile in those regions. We observed Grotthus like mechanism in our ionomer, in which the positive charge migrates within the string-like cluster without the cations actually moving.

The role of sodium bicarbonate in the nucleation of noctilucent clouds

NASA Astrophysics Data System (ADS)

Plane, J. M. C.

2000-07-01

It is proposed that a component of meteoric smoke, sodium bicarbonate (NaHCO3), provides particularly effective condensation nuclei for noctilucent clouds. This assertion is based on three conditions being met. The first is that NaHCO3 is present at sufficient concentration (+/-104 cm-3) in the upper mesosphere between 80 and 90 km. It is demonstrated that there is strong evidence for this based on recent laboratory measurements coupled with atmospheric modelling. The second condition is that the thermodynamics of NaHCO3(H2O)n cluster formation allow spontaneous nucleation to occur under mesospheric conditions at temperatures below 140 K. The Gibbs free energy changes for forming clusters with n = 1 and 2 were computed from quantum calculations using hybrid density functional/Hartree-Fock (B3LYP) theory and a large basis set with added polarization and diffuse functions. The results were then extrapolated to higher n using an established dependence of the free energy on cluster size and the free energy for the sublimation of H2O to bulk ice. A 1-dimensional model of sodium chemistry was then employed to show that spontaneous nucleation to form ice particles (n >100) should occur between 84 and 89 km in the high-latitude summer mesosphere. The third condition is that other metallic components of meteoric smoke are less effective condensation nuclei, so that the total number of potential nuclei is small relative to the amount of available H2O. Quantum calculations indicate that this is probably the case for major constituents such as Fe(OH)2, FeO3 and MgCO3.

Octahedral tilt transitions in the relaxor ferroelectric Na{sub 1/2}Bi{sub 1/2}TiO{sub 3}

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

Meyer, Kai-Christian, E-mail: meyer@mm.tu-darmstadt.de; Gröting, Melanie; Albe, Karsten

2015-07-15

The kinetics of octahedral tilt transitions in the lead-free relaxor material sodium bismuth titanate Na{sub 1/2}Bi{sub 1/2}TiO{sub 3} (NBT) is investigated by electronic structure calculations within density functional theory. Energy barriers for transitions between tetragonal, rhombohedral and orthorhombic tilts in cation configurations with [001]- and [111]-order on the A-sites are determined by nudged elastic band calculations. By tilting entire layers of octahedra simultaneously we find that the activation energy is lower for structures with 001-order compared to such with 111-order. The energetic coupling between differently tilted layers is, however, negligibly small. By introducing a single octahedral defect we create localmore » tilt disorder and find that the deformation energy of the neighboring octahedra is less in a rhombohedral than in a tetragonal structure. By successively increasing the size of clusters of orthorhombic defects in a rhombohedral matrix with 001-order, we determine a critical cluster size of about 40 Å . Thus groups of about ten octahedra can be considered as nuclei for polar nanoregions, which are the cause of the experimentally observed relaxor behavior of NBT. - Graphical abstract: Nine orthorhombic oxygen octahedral tilt defects in a rhombohedral tilt configuration. - Highlights: • Chemical order influences energy barriers of octahedral tilt transitions. • The octahedral deformation energy is lower in rhombohedral phases. • Tilt defect clusters are more likely in rhombohedral structures. • Tilt defect clusters can act as nuclei for polar nanoregions.« less

The initial stages of NaCl dissolution: Ion or ion pair solvation?

NASA Astrophysics Data System (ADS)

Klimes, Jiri; Michaelides, Angelos

2009-03-01

The interaction of water with rock salt (NaCl) is important in a wide variety of natural processes and human activities. A lot is known about NaCl dissolution at the macroscopic level but we do not yet have a detailed atomic scale picture of how salt crystals dissolve. Here we report an extensive series of density functional theory, forcefield and molecular dynamics studies of water clusters at flat and defective NaCl surfaces and NaCl clusters. The focus is on answering seemingly elementary questions such as how many water molecules are needed before it becomes favorable to extract an ion or a pair of ions from the crystal or the cluster. It turns out, however, that the answers to these questions are not so straightforward: below a certain number of water molecules (˜ 12) solvation of individual ions is less costly and above this number solvation of ion pairs is favored. These results reveal a hitherto unknown complexity in the NaCl dissolution process born out of a subtle interplay between water-water and water-ion interactions.

Structural mechanism of the formation of mineral Na-tveitite-a new type of phase with a fluorite-derivative structure-in the NaF-CaF{sub 2}-(Y,Ln)F{sub 3} natural system

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

Golubev, A. M., E-mail: fluorides@ns.crys.ras.ru; Otroshchenko, L. P.; Sobolev, B. P.

2012-03-15

Relationships between the chemical compositions and structures of the mineral tveitite from the southern Norway pegmatites (with the idealized formula Ca{sub 14}Y{sub 5}F{sub 43}) and Na-tveitite from the Rov mountain (Keivy, Kola Peninsula) Na{sub 2.5}Ca{sub 10}Ln{sub 1.5}Y{sub 5}F{sub 42} are considered. According to the structural mechanism of its formation, Na-tveitite is a nanocomposite crystal based on the crystalline matrix Ca{sub 14}Y{sub 5}F{sub 43} with the ordered arrangement of {l_brace}Ca{sub 8}[CaY{sub 5}]F{sub 69}{r_brace} clusters which contain anionic {l_brace}F{sub 13}{r_brace} cuboctahedra with F{sup 1-} at the center. When Na-tveitite is formed, 29% of these clusters are statistically replaced by Na-'Y' clusters {l_brace}[Na{submore » 0.5}(Y,Ln){sub 0.5}]{sub 14}F{sub 64}{r_brace} with {l_brace}F{sub 8}{r_brace} cubes at the center (analogs of matrix fluorite groups {l_brace}Ca{sub 14}F{sub 64}{r_brace}). This replacement gives rise to composition-imperfect (Na, Ca, 'Y') cationic positions and occupancy-deficient F positions, which correspond to {l_brace}F{sub 13}{r_brace} cuboctahedra and the {l_brace}F{sub 8}{r_brace} cubes that replace them. The difference between Na-tveitite and fluorite phases M{sub 1-x}R{sub x}F{sub 2+x} is as follows: its matrix is the structure of the ordered phase (tveitite) into which Na-containing rare earth fragments of fluorite-type structure are incorporated instead of ordered-phase structural blocks (clusters).« less

Impact of leather industries on fluoride dynamics in groundwater around a tannery cluster in South India.

PubMed

Sajil Kumar, P J

2013-03-01

The aim of this study was to investigate the controls of leather industries on fluoride contamination in and around a tannery cluster in Vaniyambadi. Hydrochemical analysis, mineral saturation indices and statistical methods were used to evaluate the intervening factors that controls the contamination processes. Fluoride in groundwater is exceeded the WHO guideline value (1.5 mg/L), in 62 % of the samples, mostly with Na-HCO3 and Na-Cl type of water. Results of the principal component analysis grouped Na, F, HCO3 and NO3 under component 1. This result was in agreement with the cross plot indicating high positive correlation between F and Na (r (2)  = 0.87), HCO3 (r (2)  = 0.84) and NO3 (r (2)  = 0.55). Fluorite (CaF2) and Halite (NaCl) was undersaturated, while calcite (CaCO3) was oversaturated for all the samples. This suggest more dissolution of F-rich minerals under the active supports of Na. Bivariate plots of Na versus Cl and Na + K versus HCO3 showed a combined origin of Na from tannery effluent as well as silicate weathering. Two major clusters, based on the Na, HCO3 and F concentration showed that groundwater is affected by tanneries and silicate weathering. Fluoride concentration in 38 % of samples (n = 5) have significantly affected by the high Na concentration from tanneries.

A bronze matryoshka: the discrete intermetalloid cluster [Sn@Cu12@Sn20](12-) in the ternary phases A12Cu12Sn21 (A = Na, K).

PubMed

Stegmaier, Saskia; Fässler, Thomas F

2011-12-14

The synthesis and crystal structure of the first ternary A-Cu-Sn intermetallic phases for the heavier alkali metals A = Na to Cs is reported. The title compounds A(12)Cu(12)Sn(21) show discrete 33-atom intermetalloid Cu-Sn clusters {Sn@Cu(12)@Sn(20)}, which are composed of {Sn(20)} pentagonal dodecahedra surrounding {Cu(12)} icosahedra with single Sn atoms at the center. Na(12)Cu(12)Sn(21) and K(12)Cu(12)Sn(21) were characterized by single-crystal XRD studies, and the successful synthesis of analogous A-Cu-Sn compounds with A = Rb and Cs is deduced from powder XRD data. The isotypic A(12)Cu(12)Sn(21) phases crystallize in the cubic space group Pn ̅3m (No. 224), with the Cu-Sn clusters adopting a face centered cubic arrangement. A formal charge of 12- can be assigned to the {Sn@Cu(12)@Sn(20)} cluster unit, and the interpretation of the title compounds as salt-like intermetallic phases featuring discrete anionic intermetalloid [Sn@Cu(12)@Sn(20)](12-) clusters separated by alkali metal cations is supported by electronic structure calculations. For both Na(12)Cu(12)Sn(21) and K(12)Cu(12)Sn(21), DFT band structure calculations (TB-LMTO-ASA) reveal a band gap. The discrete [Sn@Cu(12)@Sn(20)](12-) cluster is analyzed in consideration of the molecular orbitals obtained from hybrid DFT calculations (Gaussian 09) for the cluster anion. The [Sn@Cu(12)@Sn(20)](12-) cluster MOs can be classified with labels indicating the numbers of radial and angular nodes, in the style of spherical shell models of cluster bonding. © 2011 American Chemical Society

Cluster Morphology-Polymer Dynamics Correlations in Sulfonated Polystyrene Melts: Computational Study

DOE PAGES

Agrawal, Anupriya; Perahia, Dvora; Grest, Gary S.

2016-04-11

Reaching exceptionally long times up to 500 ns in equilibrium and nonequilibrium molecular dynamics simulations studies, we have attained a fundamental molecular understanding of the correlation of ionomer clusters structure and multiscale dynamics, providing new insight into one critical, long-standing challenge in ionic polymer physics. The cluster structure in melts of sulfonated polystyrene with Na + and Mg 2+ counterions are resolved and correlated with the dynamics on multiple length and time scales extracted from measurements of the dynamic structure factor and shear rheology. We find that as the morphology of the ionic clusters changes from ladderlike for Na +more » to disordered structures for Mg 2+, the dynamic structure factor is affected on the length scale corresponding to the ionic clusters. Lastly, rheology studies show that the viscosity for Mg 2+ melts is higher than for Na + ones for all shear rates, which is well correlated with the larger ionic clusters’ size for the Mg 2+ melts.« less

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

Johnson, Christian I.; Caldwell, Nelson; Rich, R. Michael

We present radial velocities and chemical abundances for red giant branch stars in the Galactic bulge globular clusters NGC 6342 and NGC 6366. The velocities and abundances are based on measurements of high-resolution ( R ≳ 20,000) spectra obtained with the MMT–Hectochelle and WIYN–Hydra spectrographs. We find that NGC 6342 has a heliocentric radial velocity of +112.5 km s{sup −1} ( σ = 8.6 km s{sup −1}), NGC 6366 has a heliocentric radial velocity of −122.3 km s{sup −1} ( σ = 1.5 km s{sup −1}), and both clusters have nearly identical metallicities ([Fe/H] ≈ −0.55). NGC 6366 shows evidencemore » of a moderately extended O–Na anti-correlation, but more data are needed for NGC 6342 to determine if this cluster also exhibits the typical O–Na relation likely found in all other Galactic globular clusters. The two clusters are distinguished from similar metallicity field stars as having larger [Na/Fe] spreads and enhanced [La/Fe] ratios, but we find that NGC 6342 and NGC 6366 display α and Fe-peak element abundance patterns that are typical of other metal-rich ([Fe/H] > −1) inner Galaxy clusters. However, the median [La/Fe] abundance may vary from cluster-to-cluster.« less

Na8Au9.8(4)Ga7.2 and Na17Au5.87(2)Ga46.63: The diversity of pseudo 5-fold symmetries in the Na-Au-Ga system

NASA Astrophysics Data System (ADS)

Smetana, Volodymyr; Corbett, John D.; Miller, Gordon J.

2013-11-01

The Na-rich part (~30% Na) of the Na-Au-Ga system between NaAu2, NaGa4, and Na22Ga39 has been found to contain the ternary phases Na8Au9.8(4)Ga7.2 (I) and Na17Au5.87(2)Ga46.63 (II), according to the results of single crystal X-ray diffraction measurements. I is orthorhombic, Cmcm, a=5.3040(1), b=24.519(5), c=14.573(3) Å, and contains a network of clusters with local 5-fold symmetry along the a-axis. Such clusters are frequent building units in decagonal quasicrystals and their approximants. II is rhombohedral, R3¯m, a=16.325(2), c=35.242(7) Å, and contains building blocks that are structurally identical to the Bergman-type clusters as well as fused icosahedral units known with active metals, triels and late transition elements. II also contains a polycationic network with elements of the clathrate V type structure. Tight-binding electronic structure calculations using linear muffin-tin-orbital (LMTO) methods on idealized models of I and II indicate that both compounds are metallic with evident pseudogaps at the corresponding Fermi levels. The overall Hamilton bond populations are generally dominated by Au-Ga and Au-Au bonds in I and by Ga-Ga bonds in II; moreover, the Na-Au and Na-Ga contributions in I are unexpectedly large, ~20% of the total. A similar involvement of sodium in covalent bonding has also been found in the electron-richer i-Na13Au12Ga15 quasicrystal approximant.

A ferrocenecarboxylate-functionalized titanium-oxo-cluster: the ferrocene wheel as a sensitizer for photocurrent response.

PubMed

Fan, Yang; Cui, Ying; Zou, Guo-Dong; Duan, Rui-Huan; Zhang, Xu; Dong, Yu-Xiang; Lv, Hai-Ting; Cao, Jun-Tao; Jing, Qiang-Shan

2017-06-27

Sensitized titanium-oxo clusters (TOCs) have attracted growing interest. However, reports on TOCs incorporated with a metal complex as photosensitizers are still very rare. In the present work, the organometallic complex ferrocene was used as a sensitizer for a titanium-oxo cluster. A ferrocenecarboxylate-substituted titanium-oxo cluster [Ti 6 (μ 3 -O) 6 (OiPr) 6 (O 2 CFc) 6 ] (Fc = ferrocenyl) was synthesized and structurally characterized, in which the ferrocene wheel performs as a sensitizer for photocurrent response. For comparison, naphthalene-sensitized titanium-oxo clusters [Ti 6 (μ 3 -O) 6 (OiPr) 6 (NA) 6 ] (NA = 1-naphthoate) and [Ti 6 (μ 3 -O) 6 (OiPr) 6 (NAA) 6 ] (NAA = 1-naphthylacetate) with the same {Ti 6 } core structure were also synthesized. The structures, optical behaviors, electronic states and photoelectrochemical properties of these sensitized {Ti 6 } clusters were investigated. It is demonstrated that the introduction of ferrocene groups into the titanium-oxo cluster significantly reduces the band gap and enhances the photocurrent response in comparison with the naphthalene-sensitized clusters. The substantially reduced band gap of the ferrocene-sensitized cluster was attributed to the introduction of Fe(ii) d-d transitions and the possible contribution from the Fc → {Ti 6 } charge transfer. For the naphthalene-sensitized clusters, the better electronic coupling between the dye and the {Ti 6 } core in the 1-naphthoate (NA) substituted cluster results in higher photoelectrochemical activity.

NGC 6362: THE LEAST MASSIVE GLOBULAR CLUSTER WITH CHEMICALLY DISTINCT MULTIPLE POPULATIONS

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

Mucciarelli, Alessio; Dalessandro, Emanuele; Ferraro, Francesco R.

2016-06-20

We present the first measure of Fe and Na abundances in NGC 6362, a low-mass globular cluster (GC) where first- and second-generation stars are fully spatially mixed. A total of 160 member stars (along the red giant branch (RGB) and the red horizontal branch (RHB)) were observed with the multi-object spectrograph FLAMES at the Very Large Telescope. We find that the cluster has an iron abundance of [Fe/H] = −1.09 ± 0.01 dex, without evidence of intrinsic dispersion. On the other hand, the [Na/Fe] distribution turns out to be intrinsically broad and bimodal. The Na-poor and Na-rich stars populate, respectively,more » the bluest and the reddest RGBs detected in the color–magnitude diagrams including the U filter. The RGB is composed of a mixture of first- and second-generation stars in a similar proportion, while almost all the RHB stars belong to the first cluster generation. To date, NGC 6362 is the least massive GC where both the photometric and spectroscopic signatures of multiple populations have been detected.« less

The accuracy of ab initio calculations without ab initio calculations for charged systems: Kriging predictions of atomistic properties for ions in aqueous solutions

NASA Astrophysics Data System (ADS)

Di Pasquale, Nicodemo; Davie, Stuart J.; Popelier, Paul L. A.

2018-06-01

Using the machine learning method kriging, we predict the energies of atoms in ion-water clusters, consisting of either Cl- or Na+ surrounded by a number of water molecules (i.e., without Na+Cl- interaction). These atomic energies are calculated following the topological energy partitioning method called Interacting Quantum Atoms (IQAs). Kriging predicts atomic properties (in this case IQA energies) by a model that has been trained over a small set of geometries with known property values. The results presented here are part of the development of an advanced type of force field, called FFLUX, which offers quantum mechanical information to molecular dynamics simulations without the limiting computational cost of ab initio calculations. The results reported for the prediction of the IQA components of the energy in the test set exhibit an accuracy of a few kJ/mol, corresponding to an average error of less than 5%, even when a large cluster of water molecules surrounding an ion is considered. Ions represent an important chemical system and this work shows that they can be correctly taken into account in the framework of the FFLUX force field.

Generalized vibrating potential model for collective excitations in spherical, deformed and superdeformed systems: (1) Atomic nuclei, (2) Metal clusters

NASA Astrophysics Data System (ADS)

Nesterenko, V. O.; Kleinig, W.

1995-01-01

The self-consistent vibrating potential model (VPM) is extended for description of Eλ collective excitations in atomic nuclei and metal clusters with practically any kind of static deformation. The model is convenient for a qualitative analysis and provides the RPA accuracy of numerical calculations. The VPM is applied to study Eλ giant resonances in spherical metal clusters and deformed and superdeformed nuclei. It is shown that the deformation splitting of superdeformed nuclei results in a very complicated ("jungle-like") structure of the resonances, which makes the experimental observation of E2 and E3 giant resonances in superdeformed nuclei quite problematic. Calculations of E1 giant resonances in spherical sodium clusters Na8, Na20 and Na40 are presented, as a test of the VPM in this field. The results are in qualitative agreement with the experimental data.

Influenza A Virus Hemagglutinin and Neuraminidase Mutually Accelerate Their Apical Targeting through Clustering of Lipid Rafts

PubMed Central

Ohkura, Takashi; Momose, Fumitaka; Ichikawa, Reiko; Takeuchi, Kaoru

2014-01-01

ABSTRACT In polarized epithelial cells, influenza A virus hemagglutinin (HA) and neuraminidase (NA) are intrinsically associated with lipid rafts and target the apical plasma membrane for viral assembly and budding. Previous studies have indicated that the transmembrane domain (TMD) and cytoplasmic tail (CT) of HA and NA are required for association with lipid rafts, but the raft dependencies of their apical targeting are controversial. Here, we show that coexpression of HA with NA accelerated their apical targeting through accumulation in lipid rafts. HA was targeted to the apical plasma membrane even when expressed alone, but the kinetics was much slower than that of HA in infected cells. Coexpression experiments revealed that apical targeting of HA and NA was accelerated by their coexpression. The apical targeting of HA was also accelerated by coexpression with M1 but not M2. The mutations in the outer leaflet of the TMD and the deletion of the CT in HA and NA that reduced their association with lipid rafts abolished the acceleration of their apical transport, indicating that the lipid raft association is essential for efficient apical trafficking of HA and NA. An in situ proximity ligation assay (PLA) revealed that HA and NA were accumulated and clustered in the cytoplasmic compartments only when both were associated with lipid rafts. Analysis with mutant viruses containing nonraft HA/NA confirmed these findings. We further analyzed lipid raft markers by in situ PLA and suggest a possible mechanism of the accelerated apical transport of HA and NA via clustering of lipid rafts. IMPORTANCE Lipid rafts serve as sites for viral entry, particle assembly, and budding, leading to efficient viral replication. The influenza A virus utilizes lipid rafts for apical plasma membrane targeting and particle budding. The hemagglutinin (HA) and neuraminidase (NA) of influenza virus, key players for particle assembly, contain determinants for apical sorting and lipid raft association. However, it remains to be elucidated how lipid rafts contribute to the apical trafficking and budding. We investigated the relation of lipid raft association of HA and NA to the efficiency of apical trafficking. We show that coexpression of HA and NA induces their accumulation in lipid rafts and accelerates their apical targeting, and we suggest that the accelerated apical transport likely occurs by clustering of lipid rafts at the TGN. This finding provides the first evidence that two different raft-associated viral proteins induce lipid raft clustering, thereby accelerating apical trafficking of the viral proteins. PMID:24965459

An unusual 2p-3d-4f heterometallic coordination polymer featuring Ln8Na and Cu8I clusters as nodes

NASA Astrophysics Data System (ADS)

Zhao, Mingjuan; Chen, Shimin; Huang, Yutian; Dan, Youmeng

2017-01-01

A new cluster-based three-dimensional 2p-3d-4f heterometallic framework {[Ho8Na(OH)6Cu16I2(CPT)24](NO3)9(H2O)6(CH3CN)18}n (1, HCPT = 4-(4-carboxyphenyl)-1,2,4 triazole) has been prepared under solvothermal condition by using a custom-designed bifunctional organic ligand. The single-crystal structure analysis reveals that this framework features novel Ln8Na and Cu8I clusters as nodes, these nodes are further connected by the CPT ligands to give rise to a (6,14)-connected network. The magnetic property of this framework has also been investigated.

Phytotoxicity, Translocation, and Biotransformation of NaYF₄ Upconversion Nanoparticles in a Soybean Plant.

PubMed

Yin, Wenyan; Zhou, Liangjun; Ma, Yuhui; Tian, Gan; Zhao, Jiating; Yan, Liang; Zheng, Xiaopeng; Zhang, Peng; Yu, Jie; Gu, Zhanjun; Zhao, Yuliang

2015-09-01

The increasing uses of rare-earth-doped upconversion nanoparticles (UCNPs) have obviously caused many concerns about their potential toxicology on live organisms. In addition, the UCNPs can be released into the environment, then transported into edible crop plants, and finally entered into food chain. Here, the soybean is chosen as a model plant to study the subchronic phytotoxicity, translocation, and biotransformation of NaYF4 UCNPs. The incubation with UCNPs at a relative low concentration of 10 μg mL(-1) leads to growth promotion for the roots and stems, while concentration exceeding 50 μg mL(-1) brings concentration-dependent inhibition. Upconversion luminescence imaging and scanning electron microscope characterization show that the UCNPs can be absorbed by roots and parts of the adsorbed UCNPs are then transported through vessels to stems and leaves. The near-edge X-ray absorption fine structure spectra reveal that the adsorbed NaYF4 nanoparticles are relatively stable during a 10 d incubation. Energy-dispersive X-ray spectrum further indicates that a small amount of NaYF4 is dissolved/digested and can transform into Y-phosphate clusters in roots. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Structural variation from heterometallic cluster-based 1D chain to heterometallic tetranuclear cluster: Syntheses, structures and magnetic properties

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

Zhang, Shu-Hua, E-mail: zsh720108@163.com; Zhao, Ru-Xia; Li, He-Ping

Using the solvothermal method, we present the comparative preparation of ([Co{sub 3}Na(dmaep){sub 3}(ehbd)(N{sub 3}){sub 3}]·DMF){sub n} (1) and [Co{sub 2}Na{sub 2}(hmbd){sub 4}(N{sub 3}){sub 2}(DMF){sub 2}] (2), where Hehbd is 3-ethoxy-2-hydroxy-benzaldehyde, Hhmbd is 3-methoxy-2-hydroxy-benzaldehyde, and Hdmaep is 2-dimethylaminomethyl-6-ethoxy-phenol, which was synthesized by an in-situ reaction. Complexes 1 and 2 were characterized by elemental analysis, IR spectroscopy, and X-ray single-crystal diffraction. Complex 1 is a novel heterometallic cluster-based 1-D chain and 2 is a heterometallic tetranuclear cluster. The (Co{sub 3}{sup II}Na) and (Co{sub 2}{sup II}Na{sub 2}) cores display dominant ferromagnetic interaction from the nature of the binding modes through μ{sub 1,1,1}-N{sub 3}{supmore » –} (end-on, EO). - Graphical abstract: Two novel cobalt complexes have been prepared. Compound 1 consists of tetranuclear (Co{sub 3}{sup II}Na) units, which further formed a 1-D chain. Compound 2 is heterometallic tetranuclear cluster. Two complexes display dominant ferromagnetic interaction. - Highlights: • Two new heterometallic complexes have been synthesized by solvothermal method. • The stereospecific blockade of the ligands in the synthesis system seems to be the most important synthetic parameter. • The magnetism studies show that 1 and 2 exhibit ferromagnetic interactions. • Complex 1 shows slowing down of magnetization and not blocking of magnetization.« less

Atomic and electronic structure of the silicon and silicon-metal Si{sub 20}, Si{sub 20}{sup -}, NaSi{sub 20}, KSi{sub 20} nanoparticles

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

Borshch, N. A., E-mail: ssd18@phys.vsu.ru; Pereslavtseva, N. S.; Kurganskii, S. I.

The results of atomic-structure optimization and calculation of the electronic structure of the Si{sub 20}, Si{sub 20}{sup -}, NaSi{sub 20}, and KSi{sub 20} clusters are reported. The PM3 and AM1 semiempirical methods were used in the calculations. It is shown that the Na and K atoms stabilize the fullerene-like silicon structure. The effect of configuration of the clusters on their electronic structure is analyzed.

Speciation and Structural Properties of Hydrothermal Solutions of Sodium and Potassium Sulfate Studied by Molecular Dynamics Simulations.

PubMed

Reimer, Joachim; Vogel, Frédéric; Steele-MacInnis, Matthew

2016-05-18

Aqueous solutions of salts at elevated pressures and temperatures play a key role in geochemical processes and in applications of supercritical water in waste and biomass treatment, for which salt management is crucial for performance. A major question in predicting salt behavior in such processes is how different salts affect the phase equilibria. Herein, molecular dynamics (MD) simulations are used to investigate molecular-scale structures of solutions of sodium and/or potassium sulfate, which show contrasting macroscopic behavior. Solutions of Na-SO4 exhibit a tendency towards forming large ionic clusters with increasing temperature, whereas solutions of K-SO4 show significantly less clustering under equivalent conditions. In mixed systems (Nax K2-x SO4 ), cluster formation is dramatically reduced with decreasing Na/(K+Na) ratio; this indicates a structure-breaking role of K. MD results allow these phenomena to be related to the characteristics of electrostatic interactions between K(+) and SO4 (2-) , compared with the analogous Na(+) -SO4 (2-) interactions. The results suggest a mechanism underlying the experimentally observed increasing solubility in ternary mixtures of solutions of Na-K-SO4 . Specifically, the propensity of sodium to associate with sulfate, versus that of potassium to break up the sodium-sulfate clusters, may affect the contrasting behavior of these salts. Thus, mutual salting-in in ternary hydrothermal solutions of Na-K-SO4 reflects the opposing, but complementary, natures of Na-SO4 versus K-SO4 interactions. The results also provide clues towards the reported liquid immiscibility in this ternary system. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Structure determination in 55-atom Li-Na and Na-K nanoalloys.

PubMed

Aguado, Andrés; López, José M

2010-09-07

The structure of 55-atom Li-Na and Na-K nanoalloys is determined through combined empirical potential (EP) and density functional theory (DFT) calculations. The potential energy surface generated by the EP model is extensively sampled by using the basin hopping technique, and a wide diversity of structural motifs is reoptimized at the DFT level. A composition comparison technique is applied at the DFT level in order to make a final refinement of the global minimum structures. For dilute concentrations of one of the alkali atoms, the structure of the pure metal cluster, namely, a perfect Mackay icosahedron, remains stable, with the minority component atoms entering the host cluster as substitutional impurities. At intermediate concentrations, the nanoalloys adopt instead a core-shell polyicosahedral (p-Ih) packing, where the element with smaller atomic size and larger cohesive energy segregates to the cluster core. The p-Ih structures show a marked prolate deformation, in agreement with the predictions of jelliumlike models. The electronic preference for a prolate cluster shape, which is frustrated in the 55-atom pure clusters due to the icosahedral geometrical shell closing, is therefore realized only in the 55-atom nanoalloys. An analysis of the electronic densities of states suggests that photoelectron spectroscopy would be a sufficiently sensitive technique to assess the structures of nanoalloys with fixed size and varying compositions.

Evaluation of Factors Influencing the Groundwater Chemistry in a Small Tropical Island of Malaysia

PubMed Central

Kura, Nura Umar; Ramli, Mohammad Firuz; Sulaiman, Wan Nur Azmin; Ibrahim, Shaharin; Aris, Ahmad Zaharin; Mustapha, Adamu

2013-01-01

Groun in a very complex way. In this work, multivariate statistical analysis was used to evaluate the factors controlling the groundwater chemistry of Kapas Island (Malaysia). Principal component analysis (P dwater chemistry of small tropical islands is influenced by many factors, such as recharge, weathering and seawater intrusion, among others, which interact with each other CA) was applied to 17 hydrochemical parameters from 108 groundwater samples obtained from 18 sampling sites. PCA extracted four PCs, namely seawater intrusion, redox reaction, anthropogenic pollution and weather factors, which collectively were responsible for more than 87% of the total variance of the island’s hydrochemistry. The cluster analysis indicated that three factors (weather, redox reaction and seawater intrusion) controlled the hydrochemistry of the area, and the variables were allocated to three groups based on similarity. A Piper diagram classified the island’s water types into Ca-HCO3 water type, Na-HCO3 water type, Na-SO4-Cl water type and Na-Cl water type, indicating recharge, mixed, weathering and leached from sewage and seawater intrusion, respectively. This work will provide policy makers and land managers with knowledge of the precise water quality problems affecting the island and can also serve as a guide for hydrochemistry assessments of other islands that share similar characteristics with the island in question. PMID:23648442

Metallic VS2 Monolayer Polytypes as Potential Sodium-Ion Battery Anode via ab Initio Random Structure Searching.

PubMed

Putungan, Darwin Barayang; Lin, Shi-Hsin; Kuo, Jer-Lai

2016-07-27

We systematically investigated the potential of single-layer VS2 polytypes as Na-battery anode materials via density functional theory calculations. We found that sodiation tends to inhibit the 1H-to-1T structural phase transition, in contrast to lithiation-induced transition on monolayer MoS2. Thus, VS2 can have better structural stability in the cycles of charging and discharging. Diffussion of Na atom was found to be very fast on both polytypes, with very small diffusion barriers of 0.085 eV (1H) and 0.088 eV (1T). Ab initio random structure searching was performed in order to explore stable configurations of Na on VS2. Our search found that both the V top and the hexagonal center sites are preferred adsorption sites for Na, with the 1H phase showing a relatively stronger binding. Notably, our random structures search revealed that Na clusters can form as a stacked second layer at full Na concentration, which is not reported in earlier works wherein uniform, single-layer Na adsorption phases were assumed. With reasonably high specific energy capacity (232.91 and 116.45 mAh/g for 1H and 1T phases, respectively) and open-circuit voltage (1.30 and 1.42 V for 1H and 1T phases, respectively), VS2 is a promising alternative material for Na-ion battery anodes with great structural sturdiness. Finally, we have shown the capability of the ab initio random structure searching in the assessment of potential materials for energy storage applications.

Sum Rule for a Schiff-Like Dipole Moment

NASA Astrophysics Data System (ADS)

Raduta, A. A.; Budaca, R.

The energy-weighted sum rule for an electric dipole transition operator of a Schiff type differs from the Thomas-Reiche-Kuhn (TRK) sum rule by several corrective terms which depend on the number of system components, N. For illustration the formalism was applied to the case of Na clusters. One concludes that the random phase approximation (RPA) results for Na clusters obey the modified TRK sum rule.

Helium cluster isolation spectroscopy

NASA Astrophysics Data System (ADS)

Higgins, John Paul

Clusters of helium, each containing ~103- 104 atoms, are produced in a molecular beam and are doped with alkali metal atoms (Li, Na, and K) and large organic molecules. Electronic spectroscopy in the visible and UV regions of the spectrum is carried out on the dopant species. Since large helium clusters are liquid and attain an equilibrium internal temperature of 0.4 K, they interact weakly with atoms or molecules absorbed on their surface or resident inside the cluster. The spectra that are obtained are characterized by small frequency shifts from the positions of the gas phase transitions, narrow lines, and cold vibrational temperatures. Alkali atoms aggregate on the helium cluster surface to form dimers and trimers. The spectra of singlet alkali dimers exhibit the presence of elementary excitations in the superfluid helium cluster matrix. It is found that preparation of the alkali molecules on the surface of helium clusters leads to the preferential formation of high-spin, van der Waals bound, triplet dimers and quartet trimers. Four bound-bound and two bound-free transitions are observed in the triplet manifold of the alkali dimers. The quartet trimers serve as an ideal system for the study of a simple unimolecular reaction in the cold helium cluster environment. Analysis of the lowest quartet state provides valuable insight into three-body forces in a van der Waals trimer. The wide range of atomic and molecular systems studied in this thesis constitutes a preliminary step in the development of helium cluster isolation spectroscopy, a hybrid technique combining the advantages of high resolution spectroscopy with the synthetic, low temperature environment of matrices.

Type II Cepheids: evidence for Na-O anticorrelation for BL Her type stars?

NASA Astrophysics Data System (ADS)

Kovtyukh, V.; Yegorova, I.; Andrievsky, S.; Korotin, S.; Saviane, I.; Lemasle, B.; Chekhonadskikh, F.; Belik, S.

2018-06-01

The chemical composition of 28 Population II Cepheids and one RR Lyrae variable has been studied using high-resolution spectra. The chemical composition of W Vir variable stars (with periods longer than 8 d) is typical for the halo and thick disc stars. However, the chemical composition of BL Her variables (with periods of 0.8-4 d) is drastically different, although it does not differ essentially from that of the stars belonging to globular clusters. In particular, the sodium overabundance ([Na/Fe] ≈ 0.4) is reported for most of these stars, and the Na-O anticorrelation is also possible. The evolutionary tracks for BL Her variables (with a progenitor mass value of 0.8 solar masses) indicate that mostly helium-overabundant stars (Y = 0.30-0.35) can fall into the instability strip region. We suppose that it is the helium overabundance that accounts not only for the existence of BL Her variable stars but also for the observed abnormalities in the chemical composition of this small group of pulsating variables.

A meteor ablation-cluster ion atmospheric sodium theory

NASA Technical Reports Server (NTRS)

Richter, E. S.; Sechrist, C. F., Jr.

1979-01-01

Neutral and ionic forms of sodium form narrow, well-defined layers which peak in the 90-95 km altitude region at midlatitudes. A new theory for the sodium layer is presented, which is found to be in good agreement with existing atmospheric observations as well as available laboratory measurements of rate constants. The layer is believed to result naturally from a meteor ablation source over a chemical sink with vertical transport of Na(+) playing an important role in the layer shape and variation. While the neutral chemistry is believed to consist of chemical equilibrium between Na and NaO, the ion chemistry departs from earlier studies and considers a cluster ion scheme. It is possible that higher-order cluster ions of sodium play a role in the formation of aerosols, through attachment or ion-induced nucleation processes.

Lowest-energy structures of (C60)nX (X=Li+,Na+,K+,Cl-) and (C60)nYCl (Y=Li,Na,K) clusters for n

PubMed

Hernández-Rojas, J; Bretón, J; Gomez Llorente, J M; Wales, D J

2004-12-22

Basin-hopping global optimization is used to find likely candidates for the lowest minima on the potential energy surface of (C(60))(n)X (X=Li(+),Na(+),K(+),Cl(-)) and (C(60))(n)YCl (Y=Li,Na,K) clusters with n

Multiple Aromaticity and Antiaromaticity in Silicon Clusters

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

Zhai, Hua JIN.; Kuznetsov, A E.; Boldyrev, Alexander I.

A series of silicon clusters containing four atoms but with different charge states (Si{sub 4}{sup 2+}, Si{sub 4}, Si{sub 4}{sup 2-}, and NaSi{sub 4}{sup -}) were studied by photoelectron spectroscopy and ab initio calculations. Structure evolution and chemical bonding in this series were interpreted in terms of aromaticity and antiaromaticity, which allowed the prediction of how structures of the four-atom silicon clusters change upon addition or removal of two electrons. It is shown that Si{sub 4}{sup 2+} is square-planar, analogous to the recently discovered aromatic Al{sub 4}{sup 2-} cluster. Upon addition of two electrons, neutral Si{sub 4} becomes {sigma}-antiaromatic andmore » exhibits a rhombus distortion. Adding two more electrons to Si{sub 4} leads to two energetically close structures of Si{sub 4}{sup 2-}: either a double antiaromatic parallelogram structure or an aromatic system with a butterfly distortion. Because of the electronic instability of doubly charged Si{sub 4}{sup 2-}, a stabilizing cation (Na{sup +}) was used to produce Si{sub 4}{sup 2-} in the gas phase in the form of Na{sup +}[Si{sub 4}{sup 2-}], which was characterized experimentally by photoelectron spectroscopy. Multiple antiaromaticity in the parallelogram Na{sup +}[Si{sub 4}{sup 2-}] species is highly unusual.« less

A density functional study of second-row dicarbides C2X (X = Na-Cl) with carbon monosulfide molecule: molecular structure and bonding mechanism

NASA Astrophysics Data System (ADS)

Parida, Saroj K.; Sahu, Sridhar

2018-05-01

In present work, a systematic study regarding molecular structure, and bonding mechanism of carbon monosulfide (CS) on second-row dicarbides C2X with (X = Na-Cl) has been investigated within the framework of density functional theory (DFT). In presence of carbon monosulfide molecule, the structures of C2Na, C2Mg, C2Al, and C2Si are found be changed from cyclic to linear, whereas geometries of C2P, C2S, and C2Cl clusters are almost remain unchanged. Interestingly, the bare carbon monosulfide molecule is attached with carbon site of bare C2X clusters rather than the second-row elements (X = Na-Cl). Furthermore, the nature of bonding in C2XCS clusters has been studiedthrough Bader's topological analysis of the electron charge density distribution ρ(r), Laplacian ∇2 ρ(r) and total energy density H BCP at the bond critical points (BCPs) of the clusters within the framework of the atoms in molecules theory (AIM). In C2XCS clusters, electron density at the bond critical point ρ(r) > 0.30 a.u. with negative values of Laplacian ∇2 ρ(r) indicates shared-kind of interactions between both the carbon atoms of C2X and CS molecule. In addition, we also analyze IR spectra that could assist for the experimental detection.

Microsolvation of sodium acetate in water: Anion photoelectron spectroscopy and ab initio calculations

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

Zhang, Wen-Jing; Hou, Gao-Lei; Wang, Peng

2015-08-07

To understand the microsolvation of sodium acetate (CH{sub 3}COONa, NaOAc) in water, we studied NaOAc(H{sub 2}O){sub n}{sup −} (n = 0–3) clusters by photoelectron spectroscopy. We also investigated the structures of NaOAc(H{sub 2}O){sub n}{sup −} (n = 0–5) anions and NaOAc(H{sub 2}O){sub n} (n = 0–7) neutrals by quantum chemistry calculations. By comparing the theoretical results with the photoelectron experiment, the most probable structures of NaOAc(H{sub 2}O){sub n}{sup −/0} (n = 0–3) were determined. The study also shows that, with increasing n, the solvent-separated ion pair (SSIP) structures of NaOAc(H{sub 2}O){sub n}{sup −} anions become nearly energetically degenerate with themore » contact ion pair (CIP) structures at n = 5, while the SSIP structures of the neutral NaOAc(H{sub 2}O){sub n} clusters appear at n = 6 and become dominant at n = 7.« less

Resonant Proton Capture on Sodium-23 and Elemental Variations in Globular Cluster Stars

NASA Astrophysics Data System (ADS)

Cesaratto, John Michael

Globular clusters represent some of the oldest stellar bodies in the universe. As such, they are used as testing grounds for theories of stellar evolution and nucleosynthesis. Astronomical observations have shown star-to-star abundance variation in light-mass elements in all Galactic globular clusters. Standard stellar evolution models do not predict these variations. For instance, there exists a pronounced anticorrelation between Na and O in the cluster stars that is not observed in similar, isolated field stars. The current explanations for these observations are that a preexisting massive star could have polluted the interstellar medium where a younger star was born, or that stars undergo some additional mixing beyond dredge-up. Theoreticians rely on nuclear physics input in the form of thermonuclear reaction rates to edit or propose new theories predicting these abundance anomalies. The 23Na + p reaction is a bridge between the NeNa cycle and the MgAl cycle, but large uncertainties exist in the 23Na(p, gamma)24Mg reaction rate for burning temperatures relevant to red giant branch and asymptotic giant branch stars. The uncertainties arise from an expected, but unobserved resonance at Ecmr = 138 keV. A new high-intensity, low-energy electron cyclotron resonance (ECR) ion source at the Laboratory for Experimental Nuclear Astrophysics (LENA) has increased sensitivity for measuring this reaction. After many attempts and long measurement periods, a marginal signal (90% confidence level) has been observed from the resonance and a new strength has been established. This new strength marks a factor of 70 reduction from the previous strength upper limit. The strength has also been calculated as an upper limit at 95% confidence level. New reaction rates have been calculated for the 23Na(p, gamma)24Mg and 23 Na(p, alpha)20Ne reactions and the recommended value for the 23Na(p, gamma) 24Mg rate has been reduced by over an order of magnitude at T 9 = 0.07. This will have implications for the processing of material between the NeNa and MgAl cycles in stellar models.

Globular Cluster Contributions to the Galactic Halo

NASA Astrophysics Data System (ADS)

Martell, Sarah; Grebel, Eva; Lai, David

2010-08-01

The goal of this project is to confirm chemically that globular clusters are the source of as much as half the population of the Galactic halo. Using moderate-resolution spectroscopy from the SEGUE survey, we have identified a previously unknown population of halo field giants with distinctly strong CN features. CN variations are typically only observed in globular clusters, so these stars are interpreted as immigrants to the halo that originally formed in globular clusters. In one night of Keck/HIRES time, we will obtain high-quality, high- resolution spectra for five such stars, and determine abundances of O, Na, Mg, Al, alpha, iron-peak and neutron-capture elements. With this information we can state clearly whether these unusual CN-strong halo stars carry the full abundance pattern seen in CN-strong globular cluster stars, with depleted C, O, and Mg and enhanced N, Na, and Al. This type of coarse ``chemical tagging'' will allow a clearer division of the Galactic halo into contributions from globular clusters and from dwarf galaxies, and will place constraints on theoretical models of globular cluster formation and evolution.

Quasichemical analysis of the cluster-pair approximation for the thermodynamics of proton hydration

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

Pollard, Travis; Beck, Thomas L.; Department of Physics, University of Cincinnati, Cincinnati, Ohio 45221

2014-06-14

A theoretical analysis of the cluster-pair approximation (CPA) is presented based on the quasichemical theory of solutions. The sought single-ion hydration free energy of the proton includes an interfacial potential contribution by definition. It is shown, however, that the CPA involves an extra-thermodynamic assumption that does not guarantee uniform convergence to a bulk free energy value with increasing cluster size. A numerical test of the CPA is performed using the classical polarizable AMOEBA force field and supporting quantum chemical calculations. The enthalpy and free energy differences are computed for the kosmotropic Na{sup +}/F{sup −} ion pair in water clusters ofmore » size n = 5, 25, 105. Additional calculations are performed for the chaotropic Rb{sup +}/I{sup −} ion pair. A small shift in the proton hydration free energy and a larger shift in the hydration enthalpy, relative to the CPA values, are predicted based on the n = 105 simulations. The shifts arise from a combination of sequential hydration and interfacial potential effects. The AMOEBA and quantum chemical results suggest an electrochemical surface potential of water in the range −0.4 to −0.5 V. The physical content of single-ion free energies and implications for ion-water force field development are also discussed.« less

Thermally stable solids based on endohedrally doped ZnS clusters.

PubMed

Matxain, Jon M; Piris, Mario; Lopez, Xabier; Ugalde, Jesus M

2009-01-01

The existence of inorganic, hollow, fullerene-like ZnS clusters has been theoretically predicted and then recently confirmed experimentally. These clusters were observed to trap alkali metals and halogens because the ionization energies (IE) of alkali metals are very similar to the electron affinities (EA) of halogens. This opens the possibility of forming molecular solids composed of these fullerene building blocks because the energy released due to the difference between the IE and EA would be very small. Herein we have focused on assembling bare Zn(12)S(12) and endohedral X@Zn(12)S(12)-Y@Zn(12)S(12) dimers (X = Na, K; Y = Cl, Br) by considering the square-faces-square orientation of every two adjacent clusters, which leads to a fcc cubic crystal structure in the solid. The structures were fully optimized in all cases, and their thermal stability was confirmed by ab initio thermal molecular dynamics calculations. The optimum lattice parameter of the solids was found to be around 13.8 A, which corresponds to distances of about 2.5 A between monomers, which is typical of covalent Zn-S bonds. The resulting solids are nanoporous materials similar to B(12)N(12). Due to their nanoporous structure, these zeolite-shaped solids could be used in heterogeneous catalysis and as storage materials and molecular sieves.

Photoabsorption in sodium clusters: first principles configuration interaction calculations

NASA Astrophysics Data System (ADS)

Priya, Pradip Kumar; Rai, Deepak Kumar; Shukla, Alok

2017-05-01

We present systematic and comprehensive correlated-electron calculations of the linear photoabsorption spectra of small neutral closed- and open-shell sodium clusters (Nan, n = 2 - 6), as well as closed-shell cation clusters (Nan+, n = 3, 5). We have employed the configuration interaction (CI) methodology at the full CI (FCI) and quadruple CI (QCI) levels to compute the ground, and the low-lying excited states of the clusters. For most clusters, besides the minimum energy structures, we also consider their energetically close isomers. The photoabsorption spectra were computed under the electric-dipole approximation, employing the dipole-matrix elements connecting the ground state with the excited states of each isomer. Our calculations were tested rigorously for convergence with respect to the basis set, as well as with respect to the size of the active orbital space employed in the CI calculations. These calculations reveal that as far as electron-correlation effects are concerned, core excitations play an important role in determining the optimized ground state geometries of various clusters, thereby requiring all-electron correlated calculations. But, when it comes to low-lying optical excitations, only valence electron correlation effects play an important role, and excellent agreement with the experimental results is obtained within the frozen-core approximation. For the case of Na6, the largest cluster studied in this work, we also discuss the possibility of occurrence of plasmonic resonance in the optical absorption spectrum. Supplementary material in the form of one pdf file available from the Journal web page at http://https://doi.org/10.1140/epjd/e2017-70728-3

Influence of electrolytes on the microenvironment of F127 triblock copolymer micelles: a solvation and rotational dynamics study of coumarin dyes.

PubMed

Kumbhakar, Manoj; Ganguly, Rajib

2007-04-19

Dynamic Stokes' shift and fluorescence anisotropy measurements of coumarin 153 (C153) and coumarin 151 (C151) as fluorescence probes have been carried out to understand the influence of electrolytes (NaCl and LiCl) on the hydration behavior of aqueous (ethylene oxide)100-(propylene oxide)70-(ethylene oxide)100 (EO100-PO70-EO100, F127) block copolymer micelles. A small blue shift in the fluorescence spectra of C153 has been observed in presence of electrolytes due to the dehydration of the oxyethylene chains in the PEO-PPO region, although fluorescence spectra of C151 remain unaltered. The close vicinity of bulk water for C151 probably negates the effect of dehydration in the PEO region. Fluorescence anisotropy measurements indicate a gradual increase in microviscosity with electrolyte concentrations. The partial collapse of copolymer blocks in the presence of electrolytes has been suggested as a reason for the increase in microviscosity along with the strong hydration of ions in the corona region. The interplay between the ion hydration and the mechanically trapped water content, and specific interaction of ions, such as complexation of Li+ ions with the copolymer block, is found to control solvation dynamics in the corona region. In addition to that, it has been established that Na+ ions reside deep into the corona region whereas Li+ ions prefer to reside closer to the surface. Owing to its higher lyotropicity, LiCl influences the corona hydration to a greater extent than NaCl and sets in micelle-micelle interaction above the 2 M LiCl concentration, as reflected in the saturation of solvation time constants. The formation of larger clusters of F127 micelles above 2 M LiCl has been confirmed by dynamic light scattering measurements; however, such cluster formation is not evident with NaCl.

Large heat capacity change in a protein-monovalent cation interaction.

PubMed

Guinto, E R; Di Cera, E

1996-07-09

Current views about protein-ligand interactions state that electrostatic forces drive the binding of charged species and that burial of hydrophobic and polar surfaces controls the heat capacity change associated with the reaction. For the interaction of a protein with a monovalent cation the electrostatic components are expected to be significant due to the ionic nature of the ligand, whereas the heat capacity change is expected to be small due to the size of the surface area involved in the recognition event. The physiologically important interaction of Na+ with thrombin was studied over the temperature range from 5 to 45 degrees C and the ionic strength range from 50 to 800 mM. These measurements reveal an unanticipated result that bears quite generally on studies of molecular recognition and protein folding. Binding of Na+ to thrombin is characterized by a modest dependence on ionic strength but a large and negative heat capacity change of -1.1 +/- 0.1 kcal mol-1 K-1. The small electrostatic coupling can be explained in terms of a minimal perturbation of the ionic atmosphere of the protein upon Na+ binding. The large heat capacity change, however, is difficult to reconcile with current views on the origin of this effect from surface area changes or large folding transitions coupled to binding. It is proposed that this change is linked to burial of a large cluster of water molecules in the Na+ binding pocket upon Na+ binding. Due to their reduced mobility and highly ordered structure, water molecules sequestered in the interior of a protein must have a lower heat capacity compared to those on the surface of a protein or in the bulk solvent. Hence, a binding or folding event where water molecules are buried may result in significant heat capacity changes independent of changes in exposed hydrophobic surface or coupled conformational transitions.

ON THE BIRTH MASSES OF THE ANCIENT GLOBULAR CLUSTERS

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

Conroy, Charlie; Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA

All globular clusters (GCs) studied to date show evidence for internal (star-to-star) variation in their light-element abundances (including Li, C, N, O, F, Na, Mg, Al, and probably He). These variations have been interpreted as evidence for multiple star formation episodes within GCs, with secondary episodes fueled, at least in part, by the ejecta of asymptotic giant branch (AGB) stars from a first generation of stars. A major puzzle emerging from this otherwise plausible scenario is that the fraction of stars associated with the second episode of star formation is observed to be much larger than expected for a standardmore » initial mass function. The present work investigates this tension by modeling the observed anti-correlation between [Na/Fe] and [O/Fe] for 20 Galactic GCs. If the abundance pattern of the retained AGB ejecta does not depend on GC mass at fixed [Fe/H], then a strong correlation is found between the fraction of current GC stellar mass composed of pure AGB ejecta, f{sub p} , and GC mass. This fraction varies from 0.20 at low masses (10{sup 4.5} M{sub Sun }) to 0.45 at high masses (10{sup 6.5} M{sub Sun }). The fraction of mass associated with pure AGB ejecta is directly related to the total mass of the cluster at birth; the ratio between the initial and present mass in stars can therefore be derived. Assuming a star formation efficiency of 50%, the observed Na-O anti-correlations imply that GCs were at least 10-20 times more massive at birth, a conclusion that is in qualitative agreement with previous work. These factors are lower limits because any mass-loss mechanism that removes first- and second-generation stars equally will leave f{sub p} unchanged. The mass dependence of f{sub p} probably arises because lower mass GCs are unable to retain all of the AGB ejecta from the first stellar generation. Recent observations of elemental abundances in intermediate-age Large Magellanic Cloud clusters are re-interpreted and shown to be consistent with this basic scenario. The small scatter in f{sub p} at fixed GC mass argues strongly that the process responsible for the large mass loss is internal to GCs. A satisfactory explanation of these trends is currently lacking.« less

Synthesis and Ligand-Exchange Reactions of a Tri-Tungsten Cluster with Applications in Biomedical Imaging

ERIC Educational Resources Information Center

Noey, Elizabeth; Curtis, Jeff C.; Tam, Sylvia; Pham, David M.; Jones, Ella F.

2011-01-01

In this experiment students are exposed to concepts in inorganic synthesis and various spectroscopies as applied to a tri-tungsten cluster with applications in biomedical imaging. The tungsten-acetate cluster, Na[W[superscript 3](mu-O)[subscript 2](CH[superscript 3]COO)[superscript 9

Coherent control of alkali cluster fragmentation dynamics

NASA Astrophysics Data System (ADS)

Lindinger, Albrecht; Lupulescu, Cosmin; Bartelt, Andreas; Vajda, Štefan; Wöste, Ludger

2003-06-01

Metal clusters exhibit extraordinary chemical and catalytic properties, which sensitively depend upon their size. This behavior makes them interesting candidates for the real-time analysis of ultrafast photo-induced processes—ultimately leading to coherent control scenarii. We have performed transient multi-photon ionization experiments on small alkali clusters of different size in order to probe their wave packet dynamics, structural reorientations, charge transfers and dissociative events in different vibrationally excited electronic states including their ground state. The observed processes were highly dependent on the irradiated pulse parameters, like its phase, amplitude and duration; an emphasis to employ a feedback control system for generating the optimum pulse shapes. Their spectral and temporal behavior reflects interesting properties about the investigated system and the irradiated photochemical process. We present first the vibrational dynamics of bound, dissociated, and pre-dissociated electronically excited states of alkali dimers and trimers. The scheme for observing the wave packet dynamics in the electronic ground state using stimulated Raman-pumping is shown. Since the employed pulse parameters significantly influence the efficiency of the irradiated dynamic pathways photo-induced fragmentation experiments on bifurcating reaction channels were carried out. In these experiments different branching ionization and fragmentation pathways of electronically excited Na 2K were investigated. By employing an evolutionary algorithm for optimizing the phase and amplitude of the applied laser field, the yield of the resulting parent or fragment ions could significantly be influenced and interesting features could be concluded from the obtained optimum pulse shapes revealing the characteristic molecular oscillation period. Moreover, the influence on the optimal pulse shape due to fragmentation from larger clusters into NaK is obtained. The substructure of the optimal pulse shape thereby offers new insight into the fragmentation channel during the control process. Characteristic motions of the involved wave packets are proposed, in order to explain the optimized dynamic dissociation pathways.

Reduced ternary molybdenum and tungsten sulfides and hydroprocessing catalysis therewith

DOEpatents

Hilsenbeck, S.J.; McCarley, R.E.; Schrader, G.L.; Xie, X.B.

1999-02-16

New amorphous molybdenum/tungsten sulfides with the general formula M{sup n+}{sub 2x/n}(L{sub 6}S{sub 8})S{sub x}, where L is molybdenum or tungsten and M is a ternary metal, has been developed. Characterization of these amorphous materials by chemical and spectroscopic methods (IR, Raman, PES) shows that the (M{sub 6}S{sub 8}){sup 0} cluster units are present. Vacuum thermolysis of the amorphous Na{sub 2x}(Mo{sub 6}S{sub 8})S{sub x}{hor_ellipsis}yMeOH first produces poorly crystalline NaMo{sub 6}S{sub 8} by disproportionation at 800 C and well-crystallized NaMo{sub 6}S{sub 8} at {>=} 900 C. Ion-exchange of the sodium material in methanol with soluble M{sup 2+} and M{sup 3+} salts (M=Sn, Co, Ni, Pb, La, Ho) produces the M{sup n+}{sub 2x/n}(Mo{sub 6}S{sub 8})S{sub x}{hor_ellipsis}yMeOH compounds. Additionally, the new reduced ternary molybdenum sulfides with the general formula M{sup n+}{sub 2x/n}Mo{sub 6}S{sub 8+x}(MeOH){sub y}[MMOS] (M=Sn, Co, Ni) is an effective hydrodesulfurization (HDS) catalyst both as-prepared and after a variety of pretreatment conditions. Under specified pretreatment conditions with flowing hydrogen gas, the SnMoS type catalyst can be stabilized, and while still amorphous, can be considered as ``Chevrel phase-like`` in that both contain Mo{sub 6}S{sub 8} cluster units. Furthermore, the small cation NiMoS and CoMoS type pretreated catalyst is shown to be very active HDS catalysts with rates that exceeded the model unpromoted and cobalt-promoted MoS{sub 2} catalysts. 9 figs.

Reduced ternary molybdenum and tungsten sulfides and hydroprocessing catalysis therewith

DOEpatents

Hilsenbeck, Shane J.; McCarley, Robert E.; Schrader, Glenn L.; Xie, Xiaobing

1999-02-16

New amorphous molybdenum/tungsten sulfides with the general formula M.sup.n+.sub.2x/n (L.sub.6 S.sub.8)S.sub.x, where L is molybdenum or tungsten and M is a ternary metal, has been developed. Characterization of these amorphous materials by chemical and spectroscopic methods (IR, Raman, PES) shows that the (M.sub.6 S.sub.8).sup.0 cluster units are present. Vacuum thermolysis of the amorphous Na.sub.2x (Mo.sub.6 S.sub.8)S.sub.x .multidot.yMeOH first produces poorly crystalline NaMo.sub.6 S.sub.8 by disproportionation at 800.degree. C. and well-crystallized NaMo.sub.6 S.sub.8 at .gtoreq. 900.degree. C. Ion-exchange of the sodium material in methanol with soluble M.sup.2+ and M.sup.3+ salts (M=Sn, Co, Ni, Pb, La, Ho) produces the M.sup.n+.sub.2x/n (Mo.sub.6 S.sub.8)S.sub.x .multidot.yMeOH compounds. Additionally, the new reduced ternary molybdenum sulfides with the general formula M.sup.n+.sub.2x/n Mo.sub.6 S.sub.8+x (MeOH).sub.y ›MMOS! (M=Sn, Co, Ni) is an effective hydrodesulfurization (HDS) catalyst both as-prepared and after a variety of pretreatment conditions. Under specified pretreatment conditions with flowing hydrogen gas, the SnMoS type catalyst can be stabilized, and while still amorphous, can be considered as "Chevrel phase-like" in that both contain Mo.sub.6 S.sub.8 cluster units. Furthermore, the small cation NiMoS and CoMoS type pretreated catalyst showed to be very active HDS catalysts with rates that exceeded the model unpromoted and cobalt-promoted MoS.sub.2 catalysts.

Sodium alginate ameliorates indomethacin-induced gastrointestinal mucosal injury via inhibiting translocation in rats

PubMed Central

Yamamoto, Atsuki; Itoh, Tomokazu; Nasu, Reishi; Nishida, Ryuichi

2014-01-01

AIM: To investigate the effects of sodium alginate (AL-Na) on indomethacin-induced small intestinal lesions in rats. METHODS: Gastric injury was assessed by measuring ulcerated legions 4 h after indomethacin (25 mg/kg) administration. Small intestinal injury was assessed by measuring ulcerated legions 24 h after indomethacin (10 mg/kg) administration. AL-Na and rebamipide were orally administered. Myeloperoxidase activity in the stomach and intestine were measured. Microvascular permeability, superoxide dismutase content, glutathione peroxidase activity, catalase activity, red blood cell count, white blood cell count, mucin content and enterobacterial count in the small intestine were measured. RESULTS: AL-Na significantly reduced indomethacin-induced ulcer size and myeloperoxidase activity in the stomach and small intestine. AL-Na prevented increases in microvascular permeability, superoxide dismutase content, glutathione peroxidase activity and catalase activity in small intestinal injury induced by indomethacin. AL-Na also prevented decreases in red blood cells and white blood cells in small intestinal injury induced by indomethacin. Moreover, AL-Na suppressed mucin depletion by indomethacin and inhibited infiltration of enterobacteria into the small intestine. CONCLUSION: These results indicate that AL-Na ameliorates non-steroidal anti-inflammatory drug-induced small intestinal enteritis via bacterial translocation. PMID:24627600

Nanoprecipitates and Their Strengthening Behavior in Al-Mg-Si Alloy During the Aging Process

NASA Astrophysics Data System (ADS)

Li, Hui; Liu, Wenqing

2017-04-01

The different nanoprecipitates formed in a 6061 aluminum alloy during aging at 453 K (180 °C), with or without 168 hours of pre-natural aging (NA), and the age-hardening response of the alloy were investigated by atom probe tomography (APT) and hardness testing. A hardness plateau developed between 2 and 8 hours in both the artificial aging (AA) and artificial aging with pre-natural aging (NAAA) samples. The hardness of NAAA samples was lower than that of AA samples when artificially aged for the same time. A 168-hour NA led to the formation of solute atom clusters in the matrix. The NA accelerated the precipitation kinetics of the following AA. The solute atom clusters gave the highest hardness increment per unit volume fraction. The β″ precipitates were dominant in the samples at the hardness plateau. The average normalized Mg:Si ratios of the solute atom clusters and GP zones were near 1. The average Mg:Si ratio of β″ precipitates increased from 1.3 to 1.5 upon aging for 2 hours. The microstructural evolution of samples with or without NA and its influence on the strengthening effects are discussed based on the experimental results.

Improvement in dehydrogenation of MXH4 where M = Na, Li and X = Al, B confined in CNTs: a DFT investigation

NASA Astrophysics Data System (ADS)

Meenakshi; Agnihotri, Deepak; Jeet, Kiran; Sharma, Hitesh

2016-11-01

Nanoconfinement improves dehydrogenation kinetics of complex metal hydrides. The present paper reports effect of confinement of MXH4, where M = Na, Li and X = Al, B inside carbon nanotubes (CNTs) (n, 0) n = 9-11 chirality and diameter of 7.47 Å, 7.87 Å, 8.73 Å, respectively, using Density Functional calculations. The MXH4 interacts strongly with the surface atoms of CNT (11, 0) and is found to be the smallest stable system for confinement of MXH4 clusters. The Hydrogen release energy (E Hre) of NaAlH4 decreases sharply by 68.3 % , w.r.t. pure NaAlH4 cluster when confined inside CNT(11, 0). Similarly, in CNT (11, 0) E Hre decreases by 38.1 % for LiAlH4, 12.7 % for NaBH4 and 19.1 % for LiBH4. Thus, resulting confinement had a profound effect in improving the energetics of complex metal hydride nanoparticles without catalyst.

High-resolution clustered pinhole (131)Iodine SPECT imaging in mice.

PubMed

van der Have, Frans; Ivashchenko, Oleksandra; Goorden, Marlies C; Ramakers, Ruud M; Beekman, Freek J

2016-08-01

High-resolution pre-clinical (131)I SPECT can facilitate development of new radioiodine therapies for cancer. To this end, it is important to limit resolution-degrading effects of pinhole edge penetration by the high-energy γ-photons of iodine. Here we introduce, optimize and validate (131)I SPECT performed with a dedicated high-energy clustered multi-pinhole collimator. A SPECT-CT system (VECTor/CT) with stationary gamma-detectors was equipped with a tungsten collimator with clustered pinholes. Images were reconstructed with pixel-based OSEM, using a dedicated (131)I system matrix that models the distance- and energy-dependent resolution and sensitivity of each pinhole, as well as the intrinsic detector blurring and variable depth of interaction in the detector. The system performance was characterized with phantoms and in vivo static and dynamic (131)I-NaI scans of mice. Reconstructed image resolution reached 0.6mm, while quantitative accuracy measured with a (131)I filled syringe reaches an accuracy of +3.6±3.5% of the gold standard value. In vivo mice scans illustrated a clear shape of the thyroid and biodistribution of (131)I within the animal. Pharmacokinetics of (131)I was assessed with 15-s time frames from the sequence of dynamic images and time-activity curves of (131)I-NaI. High-resolution quantitative and fast dynamic (131)I SPECT in mice is possible by means of a high-energy collimator and optimized system modeling. This enables analysis of (131)I uptake even within small organs in mice, which can be highly valuable for development and optimization of targeted cancer therapies. Copyright © 2016 Elsevier Inc. All rights reserved.

Structural diversities induced by cation sizes in a series of fluorogermanophosphates: A2[GeF2(HPO4)2] (A = Na, K, Rb, NH4, and Cs).

PubMed

Chen, Zhang-Gai; Huang, Xia; Zhuang, Rong-Chuan; Zhang, Yu; Liu, Xin; Shi, Tao; Wang, Shuai-Hua; Wu, Shao-Fan; Mi, Jin-Xiao; Huang, Ya-Xi

2017-09-12

Germanophosphates, in comparison with other metal phosphates, have been less studied but potentially exhibit more diverse structural chemistry with wide applications. Herein we applied a hydro-/solvo-fluorothermal route to make use of both the "tailor effect" of fluoride for the formation of low dimensional anionic clusters and the presence of alkali cations of different sizes to align the anionic clusters to control the overall crystal symmetries of germanophosphates. The synergetic effects of fluoride and alkali cations led to structural changes from chain-like structures to layered structures in a series of five novel fluorogermanophosphates: A 2 [GeF 2 (HPO 4 ) 2 ] (A = Na, K, Rb, NH 4 , and Cs, denoted as Na, K, Rb, NH4, and Cs). Although these fluorogermanophosphates have stoichiometrically equivalent formulas, they feature different anionic clusters, diverse structural dimensionalities, and contrasting crystal symmetries. Chain-like structures were observed for the compounds with the smaller sized alkali ions (Na + , K + , and Rb + ), whereas layered structures were found for those containing the larger sized cations ((NH 4 ) + and Cs + ). Specifically, monoclinic space groups were observed for the Na, K, Rb, and NH4 compounds, whereas a tetragonal space group P4/mbm was found for the Cs compound. These compounds provide new insights into the effects of cation sizes on the anionic clusters built from GeO 4 F 2 octahedra and HPO 4 tetrahedra as well as their influences on the overall structural symmetries in germanophosphates. Further characterization including IR spectroscopy and thermal analyses for all five compounds is also presented.

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

NASA Astrophysics Data System (ADS)

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

2013-09-01

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

Identification of the coupling step in Na(+)-translocating NADH:quinone oxidoreductase from real-time kinetics of electron transfer.

PubMed

Belevich, Nikolai P; Bertsova, Yulia V; Verkhovskaya, Marina L; Baykov, Alexander A; Bogachev, Alexander V

2016-02-01

Bacterial Na(+)-translocating NADH:quinone oxidoreductase (Na(+)-NQR) uses a unique set of prosthetic redox groups-two covalently bound FMN residues, a [2Fe-2S] cluster, FAD, riboflavin and a Cys4[Fe] center-to catalyze electron transfer from NADH to ubiquinone in a reaction coupled with Na(+) translocation across the membrane. Here we used an ultra-fast microfluidic stopped-flow instrument to determine rate constants and the difference spectra for the six consecutive reaction steps of Vibrio harveyi Na(+)-NQR reduction by NADH. The instrument, with a dead time of 0.25 ms and optical path length of 1 cm allowed collection of visible spectra in 50-μs intervals. By comparing the spectra of reaction steps with the spectra of known redox transitions of individual enzyme cofactors, we were able to identify the chemical nature of most intermediates and the sequence of electron transfer events. A previously unknown spectral transition was detected and assigned to the Cys4[Fe] center reduction. Electron transfer from the [2Fe-2S] cluster to the Cys4[Fe] center and all subsequent steps were markedly accelerated when Na(+) concentration was increased from 20 μM to 25 mM, suggesting coupling of the former step with tight Na(+) binding to or occlusion by the enzyme. An alternating access mechanism was proposed to explain electron transfer between subunits NqrF and NqrC. According to the proposed mechanism, the Cys4[Fe] center is alternatively exposed to either side of the membrane, allowing the [2Fe-2S] cluster of NqrF and the FMN residue of NqrC to alternatively approach the Cys4[Fe] center from different sides of the membrane. Copyright © 2015 Elsevier B.V. All rights reserved.

A Large C+N+O Abundance Spread in Giant Stars of the Globular Cluster NGC 1851

NASA Astrophysics Data System (ADS)

Yong, David; Grundahl, Frank; D'Antona, Francesca; Karakas, Amanda I.; Lattanzio, John C.; Norris, John E.

2009-04-01

Abundances of C, N, and O are determined in four bright red giants that span the known abundance range for light (Na and Al) and s-process (Zr and La) elements in the globular cluster NGC 1851. The abundance sum C+N+O exhibits a range of 0.6 dex, a factor of 4, in contrast to other clusters in which no significant C+N+O spread is found. Such an abundance range offers support for the Cassisi et al. scenario in which the double subgiant branch populations are coeval but with different mixtures of C+N+O abundances. Further, the Na, Al, Zr, and La abundances are correlated with C+N+O, and therefore NGC 1851 is the first cluster to provide strong support for the scenario in which asymptotic giant branch stars are responsible for the globular cluster light element abundance variations. This paper includes data gathered with the 6.5 meter Magellan Telescopes located at Las Campanas Observatory, Chile.

Abundance ratios in dwarf elliptical galaxies

NASA Astrophysics Data System (ADS)

Şen, Ş.; Peletier, R. F.; Boselli, A.; den Brok, M.; Falcón-Barroso, J.; Hensler, G.; Janz, J.; Laurikainen, E.; Lisker, T.; Mentz, J. J.; Paudel, S.; Salo, H.; Sybilska, A.; Toloba, E.; van de Ven, G.; Vazdekis, A.; Yesilyaprak, C.

2018-04-01

We determine abundance ratios of 37 dwarf ellipticals (dEs) in the nearby Virgo cluster. This sample is representative of the early-type population of galaxies in the absolute magnitude range -19.0 < Mr < -16.0. We analyse their absorption line-strength indices by means of index-index diagrams and scaling relations and use the stellar population models to interpret them. We present ages, metallicities, and abundance ratios obtained from these dEs within an aperture size of Re/8. We calculate [Na/Fe] from NaD, [Ca/Fe] from Ca4227, and [Mg/Fe] from Mgb. We find that [Na/Fe] is underabundant with respect to solar, whereas [Mg/Fe] is around solar. This is exactly opposite to what is found for giant ellipticals, but follows the trend with metallicity found previously for the Fornax dwarf NGC 1396. We discuss possible formation scenarios that can result in such elemental abundance patterns, and we speculate that dEs have disc-like star formation history (SFH) favouring them to originate from late-type dwarfs or small spirals. Na-yields appear to be very metal-dependent, in agreement with studies of giant ellipticals, probably due to the large dependence on the neutron-excess in stars. We conclude that dEs have undergone a considerable amount of chemical evolution, they are therefore not uniformly old, but have extended SFH, similar to many of the Local Group galaxies.

NGC 6535: the lowest mass Milky Way globular cluster with a Na-O anti-correlation? Cluster mass and age in the multiple population context

NASA Astrophysics Data System (ADS)

Bragaglia, A.; Carretta, E.; D'Orazi, V.; Sollima, A.; Donati, P.; Gratton, R. G.; Lucatello, S.

2017-11-01

To understand globular clusters (GCs) we need to comprehend how their formation process was able to produce their abundance distribution of light elements. In particular, we seek to figure out which stars imprinted the peculiar chemical signature of GCs. One of the best ways is to study the light-element anti-correlations in a large sample of GCs that are analysed homogeneously. As part of our spectroscopic survey of GCs with FLAMES, we present here the results of our study of about 30 red giant member stars in the low-mass, low-metallicity Milky Way cluster NGC 6535. We measured the metallicity (finding [Fe/H] =-1.95, rms = 0.04 dex in our homogeneous scale) and other elements of the cluster and, in particular, we concentrate here on O and Na abundances. These elements define the normal Na-O anti-correlation of classical GCs, making NGC 6535 perhaps the lowest mass cluster with a confirmed presence of multiple populations. We updated the census of Galactic and extragalactic GCs for which a statement on the presence or absence of multiple populations can be made on the basis of high-resolution spectroscopy preferentially, or photometry and low-resolution spectroscopy otherwise; we also discuss the importance of mass and age of the clusters as factors for multiple populations. Based on observations collected at ESO telescopes under programme 093.B-0583.Table 2 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/607/A44

Activation of human naïve Th cells increases surface expression of GD3 and induces neoexpression of GD2 that colocalize with TCR clusters.

PubMed

Villanueva-Cabello, Tania M; Mollicone, Rosella; Cruz-Muñoz, Mario E; López-Guerrero, Delia V; Martínez-Duncker, Iván

2015-12-01

CD4+ T helper lymphocytes (Th) orchestrate the immune response after their activation by antigen-presenting cells. Activation of naïve Th cells is reported to generate the reduction in surface epitopes of sialic acid (Sia) in α2,3 and α2,6 linkages. In this work, we report that in spite of this glycophenotype, anti-CD3/anti-CD28-activated purified human naïve Th cells show a significant increase in surface Sia, as assessed by metabolic labeling, compared with resting naïve Th cells, suggesting an increased flux of Sia toward Siaα2,8 glycoconjugates. To understand this increase as a result of ganglioside up-regulation, we observed that very early after activation, human naïve Th cells show an increased expression in surface GD3 and neoexpression of surface GD2 gangliosides, the latter clustering with the T cell receptor (TCR). Also, we report that in contrast to GM2/GD2 synthase null mice, lentiviral vector-mediated silencing of the GM2/GD2 synthase in activated human naïve Th cells reduced efficient TCR clustering and downstream signaling, as assessed by proliferation assays and IL-2 and IL-2R expression, pointing to an important role of this enzyme in activation of human naive Th cells. © The Author 2015. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Exploring the Chemical Composition and Double Horizontal Branch of the Bulge Globular Cluster NGC 6569

NASA Astrophysics Data System (ADS)

Johnson, Christian I.; Rich, R. Michael; Caldwell, Nelson; Mateo, Mario; Bailey, John I., III; Olszewski, Edward W.; Walker, Matthew G.

2018-02-01

Photometric and spectroscopic analyses have shown that the Galactic bulge cluster Terzan 5 hosts several populations with different metallicities and ages that manifest as a double red horizontal branch (HB). A recent investigation of the massive bulge cluster NGC 6569 revealed a similar, though less extended, HB luminosity split, but little is known about the cluster’s detailed chemical composition. Therefore, we have used high-resolution spectra from the Magellan–M2FS and VLT–FLAMES spectrographs to investigate the chemical compositions and radial velocity distributions of red giant branch and HB stars in NGC 6569. We found the cluster to have a mean heliocentric radial velocity of ‑48.8 km s‑1 (σ = 5.3 km s‑1 148 stars) and < [{Fe}/{{H}}]> =-0.87 dex (19 stars), but the cluster’s 0.05 dex [Fe/H] dispersion precludes a significant metallicity spread. NGC 6569 exhibits light- and heavy-element distributions that are common among old bulge/inner Galaxy globular clusters, including clear (anti)correlations between [O/Fe], [Na/Fe], and [Al/Fe]. The light-element data suggest that NGC 6569 may be composed of at least two distinct populations, and the cluster’s low < [{La}/{Eu}]> =-0.11 dex indicates significant pollution with r-process material. We confirm that both HBs contain cluster members, but metallicity and light-element variations are largely ruled out as sources for the luminosity difference. However, He mass fraction differences as small as ΔY ∼ 0.02 cannot be ruled out and may be sufficient to reproduce the double HB.

Tetravalent Ce in the Nitrate-Decorated Hexanuclear Cluster [Ce 6 (μ 3 -O) 4 (μ 3 -OH) 4 ] 12+ : A Structural End Point for Ceria Nanoparticles

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

Estes, Shanna L.; Antonio, Mark R.; Soderholm, L.

2016-03-17

We describe the synthesis and characterization of three glycine-stabilized hexanuclear Cely cluster compounds, each containing the [Ce-6(mu(3)-O)(4)(mu(3)-OH)(4)](12+) core structure. Crystallized from aqueous nitrate solutions with pH < 0, the core cluster structures exhibit variable decoration by nitrate, glycine, and water ligands depending on solution conditions, where increased nitrate and glycine decoration of the cluster core was observed for crystals synthesized at high Ce and nitrate concentrations. No other crystalline products were observed using this synthetic route. In addition to confirming the tetravalent oxidation state of cerium in one of the reported clusters, cyclic voltammetry also indicates that Ce-IV is reducedmore » at similar to+0.60 V vs Ag/AgCl (3 M NaCl), which is significantly less than the standard electrode potential. This large decrease in the Ce-IV/Ce-III reduction potential suggests that Ce-IV is significantly stabilized relative to Ce-III within the examined cluster. These compounds are discussed in terms of their importance as small, end member, ceric oxide nanoparticles. Single-crystal structural solutions, together with voltammetry and electrolysis data, permit the decoupling of Ce-III defects and substoichiometry. In addition, Ce-Ce distances can be used to determine an "effective" CeO2-x lattice constant, providing a simple method for comparing literature descriptions. The results are discussed in terms of their potential implications for the mechanisms by which nanoparticle ceria serve as catalysts and oxygen-storage materials.« less

The potassium abundance in the globular clusters NGC 104, NGC 6752 and NGC 6809

NASA Astrophysics Data System (ADS)

Mucciarelli, A.; Merle, T.; Bellazzini, M.

2017-04-01

We derived potassium abundances in red-giant-branch stars in the Galactic globular clusters NGC 104 (144 stars), NGC 6752 (134 stars), and NGC 6809 (151 stars) using high-resolution spectra collected with FLAMES at the ESO - Very Large Telescope. In the samples we consider, we do not find significant intrinsic spreads in [K/Fe], which confirms the previous findings, but which is at variance with the cases of the massive clusters NGC 2419 and NGC 2808. Additionally, marginally significant [K/Fe]-[O/Fe] anti-correlations are found in NGC 104 and NGC 6809, and [K/Fe]-[Na/Fe] correlations are found in NGC 104 and NGC 6752. No evidence of [K/Fe]-[Mg/Fe] anti-correlation are found. The results of our analysis are consistent with a scenario in which the process leading to the multi-populations in globular clusters also implies enrichment in the K abundance, the amplitude of the associated [K/Fe] enhancement becoming measurable only in stars showing the most extreme effects of O and Mg depletion. Stars enhanced in [K/Fe] have so far only been found in clusters harbouring some Mg-poor stars, while the other globulars, without a Mg-poor sub-population, show small or null [K/Fe] spreads. Full Table 1 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/600/A104

Solving the scalability issue in quantum-based refinement: Q|R#1.

PubMed

Zheng, Min; Moriarty, Nigel W; Xu, Yanting; Reimers, Jeffrey R; Afonine, Pavel V; Waller, Mark P

2017-12-01

Accurately refining biomacromolecules using a quantum-chemical method is challenging because the cost of a quantum-chemical calculation scales approximately as n m , where n is the number of atoms and m (≥3) is based on the quantum method of choice. This fundamental problem means that quantum-chemical calculations become intractable when the size of the system requires more computational resources than are available. In the development of the software package called Q|R, this issue is referred to as Q|R#1. A divide-and-conquer approach has been developed that fragments the atomic model into small manageable pieces in order to solve Q|R#1. Firstly, the atomic model of a crystal structure is analyzed to detect noncovalent interactions between residues, and the results of the analysis are represented as an interaction graph. Secondly, a graph-clustering algorithm is used to partition the interaction graph into a set of clusters in such a way as to minimize disruption to the noncovalent interaction network. Thirdly, the environment surrounding each individual cluster is analyzed and any residue that is interacting with a particular cluster is assigned to the buffer region of that particular cluster. A fragment is defined as a cluster plus its buffer region. The gradients for all atoms from each of the fragments are computed, and only the gradients from each cluster are combined to create the total gradients. A quantum-based refinement is carried out using the total gradients as chemical restraints. In order to validate this interaction graph-based fragmentation approach in Q|R, the entire atomic model of an amyloid cross-β spine crystal structure (PDB entry 2oNA) was refined.

Structure and Magnetic Properties of a Dodecanuclear Twisted-Ring Iron(III) Cluster.

PubMed

Caneschi, Andrea; Cornia, Andrea; Fabretti, Antonio C; Gatteschi, Dante

1999-05-03

An unprecedented nonplanar structure characterizes the complex [Fe(OCH 3 ) 2 (dbm)] 12 (on the left in the picture), which contains the largest cyclic ferric cluster yet reported with chemically equivalent bridging units. It is made up of twelve high-spin, antiferromagnetically coupled iron(III) centers and neatly reacts with Na I or Li I templates in organic solution to give hexairon(III) coronates (right). Fe=•, O=○, NaI or LiI=• Hdbm=dibenzoylmethane. © 1999 WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany.

SBA Innovation Clusters

DTIC Science & Technology

2012-03-02

Programs and services to help you start, grow and succeed www.sba.gov U.S. Small Business Administration Your Small Business Resource 1Approved for...Public Release SBA Innovation Clusters RADM Steven G. Smith USN (Ret) Advanced Defense Technology Cluster Coordinator U.S. Small Business ...UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) U.S. Small Business Administration ,Advanced Defense Technology Cluster,409 3rd St, SW

A remarkably stable TipE gene cluster: evolution of insect Para sodium channel auxiliary subunits

PubMed Central

2011-01-01

Background First identified in fruit flies with temperature-sensitive paralysis phenotypes, the Drosophila melanogaster TipE locus encodes four voltage-gated sodium (NaV) channel auxiliary subunits. This cluster of TipE-like genes on chromosome 3L, and a fifth family member on chromosome 3R, are important for the optional expression and functionality of the Para NaV channel but appear quite distinct from auxiliary subunits in vertebrates. Here, we exploited available arthropod genomic resources to trace the origin of TipE-like genes by mapping their evolutionary histories and examining their genomic architectures. Results We identified a remarkably conserved synteny block of TipE-like orthologues with well-maintained local gene arrangements from 21 insect species. Homologues in the water flea, Daphnia pulex, suggest an ancestral pancrustacean repertoire of four TipE-like genes; a subsequent gene duplication may have generated functional redundancy allowing gene losses in the silk moth and mosquitoes. Intronic nesting of the insect TipE gene cluster probably occurred following the divergence from crustaceans, but in the flour beetle and silk moth genomes the clusters apparently escaped from nesting. Across Pancrustacea, TipE gene family members have experienced intronic nesting, escape from nesting, retrotransposition, translocation, and gene loss events while generally maintaining their local gene neighbourhoods. D. melanogaster TipE-like genes exhibit coordinated spatial and temporal regulation of expression distinct from their host gene but well-correlated with their regulatory target, the Para NaV channel, suggesting that functional constraints may preserve the TipE gene cluster. We identified homology between TipE-like NaV channel regulators and vertebrate Slo-beta auxiliary subunits of big-conductance calcium-activated potassium (BKCa) channels, which suggests that ion channel regulatory partners have evolved distinct lineage-specific characteristics. Conclusions TipE-like genes form a remarkably conserved genomic cluster across all examined insect genomes. This study reveals likely structural and functional constraints on the genomic evolution of insect TipE gene family members maintained in synteny over hundreds of millions of years of evolution. The likely common origin of these NaV channel regulators with BKCa auxiliary subunits highlights the evolutionary plasticity of ion channel regulatory mechanisms. PMID:22098672

Long range intermolecular interactions between the alkali diatomics Na2, K2, and NaK

NASA Astrophysics Data System (ADS)

Zemke, Warren T.; Byrd, Jason N.; Michels, H. Harvey; Montgomery, John A.; Stwalley, William C.

2010-06-01

Long range interactions between the ground state alkali diatomics Na2-Na2, K2-K2, Na2-K2, and NaK-NaK are examined. Interaction energies are first determined from ab initio calculations at the coupled-cluster with singles, doubles, and perturbative triples [CCSD(T)] level of theory, including counterpoise corrections. Long range energies calculated from diatomic molecular properties (polarizabilities and dipole and quadrupole moments) are then compared with the ab initio energies. A simple asymptotic model potential ELR=Eelec+Edisp+Eind is shown to accurately represent the intermolecular interactions for these systems at long range.

Long range intermolecular interactions between the alkali diatomics Na(2), K(2), and NaK.

PubMed

Zemke, Warren T; Byrd, Jason N; Michels, H Harvey; Montgomery, John A; Stwalley, William C

2010-06-28

Long range interactions between the ground state alkali diatomics Na(2)-Na(2), K(2)-K(2), Na(2)-K(2), and NaK-NaK are examined. Interaction energies are first determined from ab initio calculations at the coupled-cluster with singles, doubles, and perturbative triples [CCSD(T)] level of theory, including counterpoise corrections. Long range energies calculated from diatomic molecular properties (polarizabilities and dipole and quadrupole moments) are then compared with the ab initio energies. A simple asymptotic model potential E(LR)=E(elec)+E(disp)+E(ind) is shown to accurately represent the intermolecular interactions for these systems at long range.

Probing the early stages of salt nucleation—experimental and theoretical investigations of sodium/potassium thiocyanate cluster anions

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

Deng, Shihu; Kong, Xiangyu; Wang, Xue B.

2015-01-14

Due to fast solvent evaporation in electrospray ionization (ESI), the concentration of initially dilute electrolyte solutions rapidly increases to afford formation of supersaturated droplets and generating various pristine anhydrous salt clusters in the gas phase. The size, composition, and charge distributions of these clusters, in principle witness the nucleation evolution in solutions. Herein, we report a microscopic study on the initial stage of nucleation and crystallization of sodium/potassium thiocyanate salt solutions simulated in the ESI process. Singly charged M x(SCN)⁻ x+1, doubly charged M y(SCN)²⁻ y+2 (M = Na, K), and triply charged K z(SCN)³⁻ z+3 anion clusters were producedmore » via electrospray of the corresponding salt solutions, and were characterized by negative ion photoelectron spectroscopy (NIPES). The vertical detachment energies (VDEs) of these sodium/potassium thiocyanate cluster anions were obtained, and theoretical calculations were carried out for sodium thiocyanate clusters in assisting spectral identification. The measured VDEs of singly charged anions M x(SCN)⁻ x+1 (M = Na and K) demonstrate they are superhalogen anions. The existence of doubly charged anions M y (SCN)²⁻ y+2 (y = 2x, x ≥ 4 and 3 for M = Na and K, respectively) and triply charged anions K z(SCN)³⁻ z+3 (z = 3x, x ≥ 6) were initially discovered from the photoelectron spectra for those singly charged anions of Msub>x(SCN)⁻ x+1 with the same mass-to-charge ratio (m/z), and later independently confirmed by observation of their distinct mass spectral distributions and by taking their NIPE spectra for those pure multiply charged anions with their m/z different from the singly charged species. For large clusters, multiply charged clusters are found to become preferred, but at higher temperatures those multiply charged clusters are suppressed. The series of anion clusters investigated here range from molecular-like M₁(SCN)⁻ 2 to nano-sized K₂₂(SCN)³⁻ 25, providing a vivid molecular-level growth pattern reflecting the initial salt nucleation process.« less

The Chemical Composition Contrast between M3 and M13 Revisited: New Abundances for 28 Giant Stars in M3

NASA Astrophysics Data System (ADS)

Sneden, Christopher; Kraft, Robert P.; Guhathakurta, Puragra; Peterson, Ruth C.; Fulbright, Jon P.

2004-04-01

We report new chemical abundances of 23 bright red giant members of the globular cluster M3, based on high-resolution (R~45,000) spectra obtained with the Keck I telescope. The observations, which involve the use of multislits in the HIRES Keck I spectrograph, are described in detail. Combining these data with a previously reported small sample of M3 giants obtained with the Lick 3 m telescope, we compare metallicities and [X/Fe] ratios for 28 M3 giants with a 35-star sample in the similar-metallicity cluster M13, and with Galactic halo field stars having [Fe/H]<-1. For elements having atomic number A>=A(Si), we derive little difference in [X/Fe] ratios in the M3, M13, or halo field samples. All three groups exhibit C depletion with advancing evolutionary state beginning at the level of the red giant branch ``bump,'' but the overall depletion of about 0.7-0.9 dex seen in the clusters is larger than that associated with the field stars. The behaviors of O, Na, Mg, and Al are distinctively different among the three stellar samples. Field halo giants and subdwarfs have a positive correlation of Na with Mg, as predicted from explosive or hydrostatic carbon burning in Type II supernova sites. Both M3 and M13 show evidence of high-temperature proton-capture synthesis from the ON, NeNa, and MgAl cycles, while there is no evidence for such synthesis among halo field stars. But the degree of such extreme proton-capture synthesis in M3 is smaller than it is in M13: the M3 giants exhibit only modest deficiencies of O and corresponding enhancements of Na, less extreme overabundances of Al, fewer stars with low Mg and correspondingly high Na, and no indication that O depletions are a function of advancing evolutionary state, as has been claimed for M13. We have also considered NGC 6752, for which Mg isotopic abundances have been reported by Yong et al. Giants in NGC 6752 and M13 satisfy the same anticorrelation of O abundances with the ratio (25Mg+26Mg)/24Mg, which measures the relative contribution of rare to abundant isotopes of Mg. This points to a scenario in which these abundance ratios arose in the ejected material of 3-6 Msolar cluster stars, material that was then used to form the atmospheres of the presently evolving low-mass cluster stars. It also suggests that the low oxygen abundance seen among the most evolved M13 giants arose in hot bottom O-to-N processing in these same intermediate-mass cluster stars. Thus, mixing is required by the dependence of some abundance ratios on luminosity, but an earlier nucleosynthesis process in a hotter environment than giants or main-sequence stars is required by the variations previously seen in stars near the main sequence. The nature and the site of the earlier process is constrained but not pinpointed by the observed Mg isotopic ratio. Based on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

Water quality analysis of the Rapur area, Andhra Pradesh, South India using multivariate techniques

NASA Astrophysics Data System (ADS)

Nagaraju, A.; Sreedhar, Y.; Thejaswi, A.; Sayadi, Mohammad Hossein

2017-10-01

The groundwater samples from Rapur area were collected from different sites to evaluate the major ion chemistry. The large number of data can lead to difficulties in the integration, interpretation, and representation of the results. Two multivariate statistical methods, hierarchical cluster analysis (HCA) and factor analysis (FA), were applied to evaluate their usefulness to classify and identify geochemical processes controlling groundwater geochemistry. Four statistically significant clusters were obtained from 30 sampling stations. This has resulted two important clusters viz., cluster 1 (pH, Si, CO3, Mg, SO4, Ca, K, HCO3, alkalinity, Na, Na + K, Cl, and hardness) and cluster 2 (EC and TDS) which are released to the study area from different sources. The application of different multivariate statistical techniques, such as principal component analysis (PCA), assists in the interpretation of complex data matrices for a better understanding of water quality of a study area. From PCA, it is clear that the first factor (factor 1), accounted for 36.2% of the total variance, was high positive loading in EC, Mg, Cl, TDS, and hardness. Based on the PCA scores, four significant cluster groups of sampling locations were detected on the basis of similarity of their water quality.

Robustness of cluster synchronous patterns in small-world networks with inter-cluster co-competition balance

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

Zhang, Jianbao; Ma, Zhongjun, E-mail: mzj1234402@163.com; Chen, Guanrong

All edges in the classical Watts and Strogatz's small-world network model are unweighted and cooperative (positive). By introducing competitive (negative) inter-cluster edges and assigning edge weights to mimic more realistic networks, this paper develops a modified model which possesses co-competitive weighted couplings and cluster structures while maintaining the common small-world network properties of small average shortest path lengths and large clustering coefficients. Based on theoretical analysis, it is proved that the new model with inter-cluster co-competition balance has an important dynamical property of robust cluster synchronous pattern formation. More precisely, clusters will neither merge nor split regardless of adding ormore » deleting nodes and edges, under the condition of inter-cluster co-competition balance. Numerical simulations demonstrate the robustness of the model against the increase of the coupling strength and several topological variations.« less

Robustness of cluster synchronous patterns in small-world networks with inter-cluster co-competition balance

NASA Astrophysics Data System (ADS)

Zhang, Jianbao; Ma, Zhongjun; Chen, Guanrong

2014-06-01

All edges in the classical Watts and Strogatz's small-world network model are unweighted and cooperative (positive). By introducing competitive (negative) inter-cluster edges and assigning edge weights to mimic more realistic networks, this paper develops a modified model which possesses co-competitive weighted couplings and cluster structures while maintaining the common small-world network properties of small average shortest path lengths and large clustering coefficients. Based on theoretical analysis, it is proved that the new model with inter-cluster co-competition balance has an important dynamical property of robust cluster synchronous pattern formation. More precisely, clusters will neither merge nor split regardless of adding or deleting nodes and edges, under the condition of inter-cluster co-competition balance. Numerical simulations demonstrate the robustness of the model against the increase of the coupling strength and several topological variations.

Path integral Monte Carlo study on the structure and absorption spectra of alkali atoms (Li, Na, K) attached to superfluid helium clusters

NASA Astrophysics Data System (ADS)

Nakayama, Akira; Yamashita, Koichi

2001-01-01

Path integral Monte Carlo calculations have been performed to investigate the microscopic structure and thermodynamic properties of the AkṡHeN (Ak=Li, Na, K,N⩽300) clusters at T=0.5 K. Absorption spectra which correspond to the 2P←2S transitions of alkali atoms are also calculated within a pairwise additive model, which employs diatomic Ak-He potential energy curves. The size dependences of the cluster structure and absorption spectra that show the influence of the helium cluster environment are examined in detail. It is found that alkali atoms are trapped in a dimple on the helium cluster's surface and that, from the asymptotic behavior, the AkṡHe300 cluster, at least semiquantitatively, mimics the local structure of experimentally produced large helium clusters in the vicinity of alkali atoms. We have successfully reproduced the overall shapes of the spectra and explained their features from a static and structural point of view. The positions, relative intensities, and line widths of the absorption maxima are calculated to be in moderate agreement with experiments [F. Stienkemeier, J. Higgins, C. Callegari, S. I. Kanorsky, W. E. Ernst, and G. Scoles, Z. Phys. D 38, 253 (1996)].

Optimizing long-range order, band gap, and group velocities for graphene on close-packed metal surfaces.

PubMed

Natterer, F D; Rusponi, S; Papagno, M; Carbone, C; Brune, H

2012-08-08

We compare different growth methods with the aim of optimizing the long-range order of a graphene layer grown on Ru(0001). Combining chemical vapor deposition with carbon loading and segregation of the surface layer leads to autocorrelation lengths of 240 Å. We present several routes to band gap and charge carrier mobility engineering for the example of graphene on Ir(111). Ir cluster superlattices self-assembled onto the graphene moiré pattern produce a strong renormalization of the electron group velocity close to the Dirac point, leading to highly anisotropic Dirac cones and the enlargement of the gap from 140 to 340 meV. This gap can further be enhanced to 740 meV by Na co-adsorption onto the Ir cluster superlattice at room temperature. This value is close to that of Ge, and the high group velocity of the charge carriers is fully preserved. We also present data for Na adsorbed without the Ir clusters. In both cases we find that the Na is on top of the graphene layer.

Intolerance of uncertainty and post-traumatic stress symptoms: An investigation within a treatment seeking trauma-exposed sample.

PubMed

Oglesby, Mary E; Gibby, Brittany A; Mathes, Brittany M; Short, Nicole A; Schmidt, Norman B

2017-01-01

Intolerance of uncertainty (IU) has been associated with post-traumatic stress symptoms (PTSS) in the literature. However, no research to date has investigated the relationship between IU and PTSS within a clinical trauma-exposed sample, which is an important next step in the literature and crucial for the generalizability of these findings. Therefore, the current study hypothesized that IU would be related to increased PTSS within a clinical sample of trauma-exposed individuals. Further, we hypothesized that IU would be related to elevated PTSS after accounting for anxiety sensitivity (AS) and negative affect (NA), two known correlates of PTSS. Finally, we examined the relations between IU and the PTSS clusters (i.e., avoidance, emotional numbing, hyperarousal, and re-experiencing) while covarying for AS and NA. Participants included community adults (n=126) presenting at an outpatient clinic. All participants had previously experienced a traumatic event as defined by the DSM-5 PTSD Criterion A. Results revealed that IU was significantly associated with increased PTSS above and beyond AS and NA. Further, results indicated that IU was significantly related to the avoidance, hyperarousal, and emotional numbing PTSS clusters, even after covarying for AS and NA. IU was not significantly associated with the PTSS re-experiencing cluster once AS and NA were taken into account. Our results expand upon the extant literature by demonstrating that IU is associated with PTSS above and beyond AS and NA within a clinical trauma-exposed sample. These findings are discussed in terms of promising directions for future research and treatment strategies. Copyright © 2016 Elsevier Inc. All rights reserved.

On 7Li Enrichment by Low-Mass Metal-Poor Red Giant Branch Stars.

PubMed

de La Reza R; da Silva L; Drake; Terra

2000-06-01

First-ascent red giants with strong and very strong Li lines have just been discovered in globular clusters. Using the stellar internal prompt (7)Li enrichment-mass-loss scenario, we explore the possibility of (7)Li enrichment in the interstellar matter of the globular cluster M3 produced by these Li-rich giants. We found that enrichment as large as 70% or more compared to the initial (7)Li content of M3 can be obtained during the entire life of this cluster. However, because M3 will cross into the Galactic plane several times, the new (7)Li will be very probably removed by ram pressure into the disk. Globular clusters appear then as possible new sources of (7)Li in the Galactic disk. It is also suggested that the known Na/Al variations in stars of globular clusters could be somehow related to the (7)Li variations and that the cool bottom process mixing mechanism acting in the case of (7)Li could also play a role in the case of Na and Al surface enrichments.

Density-based clustering of small peptide conformations sampled from a molecular dynamics simulation.

PubMed

Kim, Minkyoung; Choi, Seung-Hoon; Kim, Junhyoung; Choi, Kihang; Shin, Jae-Min; Kang, Sang-Kee; Choi, Yun-Jaie; Jung, Dong Hyun

2009-11-01

This study describes the application of a density-based algorithm to clustering small peptide conformations after a molecular dynamics simulation. We propose a clustering method for small peptide conformations that enables adjacent clusters to be separated more clearly on the basis of neighbor density. Neighbor density means the number of neighboring conformations, so if a conformation has too few neighboring conformations, then it is considered as noise or an outlier and is excluded from the list of cluster members. With this approach, we can easily identify clusters in which the members are densely crowded in the conformational space, and we can safely avoid misclustering individual clusters linked by noise or outliers. Consideration of neighbor density significantly improves the efficiency of clustering of small peptide conformations sampled from molecular dynamics simulations and can be used for predicting peptide structures.

Hydrothermal synthesis and structural characterization of an organic–inorganic hybrid sandwich-type tungstoantimonate [Cu(en){sub 2}(H{sub 2}O)]{sub 4}[Cu(en){sub 2}(H{sub 2}O){sub 2}][Cu{sub 2}Na{sub 4}(α-SbW{sub 9}O{sub 33}){sub 2}]·6H{sub 2}O

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

Liu, Yingjie; College of Medicine, Henan University, Kaifeng, Henan 475004; Cao, Jing

An organic–inorganic hybrid sandwich-type tungstoantimonate [Cu(en){sub 2}(H{sub 2}O)]{sub 4}[Cu(en){sub 2}(H{sub 2}O){sub 2}][Cu{sub 2}Na{sub 4}(α-SbW{sub 9}O{sub 33}){sub 2}]·6H{sub 2}O (1) has been synthesized by reaction of Sb{sub 2}O{sub 3}, Na{sub 2}WO{sub 4}·2H{sub 2}O, CuCl{sub 2}·2H{sub 2}O with en (en=ethanediamine) under hydrothermal conditions and structurally characterized by elemental analysis, inductively coupled plasma atomic emission spectrometry, IR spectrum and single-crystal X-ray diffraction. 1 displays a centric dimeric structure formed by two equivalent trivacant Keggin [α-SbW{sub 9}O{sub 33}]{sup 9−} subunits sandwiching a hexagonal (Cu{sub 2}Na{sub 4}) cluster. Moreover, those related hexagonal hexa-metal cluster sandwiched tungstoantimonates have been also summarized and compared. The variable-temperature magneticmore » measurements of 1 exhibit the weak ferromagnetic exchange interactions within the hexagonal (Cu{sub 2}Na{sub 4}) cluster mediated by the oxygen bridges. - Graphical abstract: An organic–inorganic hybrid (Cu{sub 2}Na{sub 4}) sandwiched tungstoantimonate [Cu(en){sub 2}(H{sub 2}O)]{sub 4}[Cu (en){sub 2}(H{sub 2}O){sub 2}][Cu{sub 2}Na{sub 4}(α-SbW{sub 9}O{sub 33}){sub 2}]·6H{sub 2}O was synthesized and magnetic properties was investigated. Display Omitted - Highlights: • Organic–inorganic hybrid sandwich-type tungstoantimonate. • (Cu{sub 2}Na{sub 4} sandwiched) tungstoantimonate [Cu{sub 2}Na{sub 4}(α-SbW{sub 9}O{sub 33}){sub 2}]{sup 10−}. • Ferromagnetic tungstoantimonate.« less

Globular Cluster Star Classification: Application to M13

NASA Astrophysics Data System (ADS)

Caimmi, R.

2013-06-01

Starting from recent determination of Fe, O, Na abundances on a restricted sample (N=67) of halo and thick disk stars, a natural and well motivated selection criterion is defined for the classification globular cluster stars. An application is performed to M13 using a sample (N=113) for which Fe, O, Na abundances have been recently inferred from observations. A comparison is made between the current and earlier M13 star classifications. Both O and Na empirical differential abundance distributions are determined for each class and for the whole sample (with the addition of Fe in the last case) and compared with their theoretical counterparts due to cosmic scatter obeying a Gaussian distribution whose parameters are inferred from related subsamples. The occurrence of an agreement between the empirical and theoretical distributions is interpreted as absence of significant chemical evolution and vice versa. The procedure is repeated with regard to four additional classes depending on whether oxygen and sodium abundance is above (stage CE) or below (stage AF) a selected threshold. Both O and Na empirical differential abundance distributions, related to the whole sample, exhibit a linear fit for the AF and CE stage. Within the errors, the oxygen slope for the CE stage is equal and of opposite sign with respect to the sodium slope for AF stage, while the contrary holds when dealing with the oxygen slope for the AF stage with respect to the sodium slope for the CE stage. In the light of simple models of chemical evolution applied to M13, oxygen depletion appears to be mainly turned into sodium enrichment for [O/H]≥-1.35 and [Na/H]≤-1.45, while one or more largely preferred channels occur for [O/H]<-1.35 and [Na/H]>-1.45. In addition, the primordial to the current M13 mass ratio can be inferred from the true sodium yield in units of the sodium solar abundance. Though the above results are mainly qualitative due to large (∓.5 dex) uncertainties in abundance determination, still the exhibited trend is expected to be real. The proposed classification of globular cluster stars may be extended in a twofold manner, namely to: (i) elements other than Na and Fe and (ii) globular clusters other than M13.

Influence of O-Co-O layer thickness on the thermal conductivity of Na{sub x}Co{sub 2}O{sub 4} studied by positron annihilation

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

Li, H. Q.; Zhao, B.; Zhang, T.

2015-07-21

Nominal stoichiometric Na{sub x}Co{sub 2}O{sub 4} (x = 1.0, 1.2, 1.4, 1.6, 1.8, and 2.0) polycrystals were synthesized by a solid-state reaction method. They were further pressed into pellets by the spark plasma sintering. The crystal structure and morphology of Na{sub x}Co{sub 2}O{sub 4} samples were characterized by X-ray diffraction and scanning electron microscopy measurements. Good crystallinity and layered structures were observed for all the samples. Positron annihilation measurements were performed for Na{sub x}Co{sub 2}O{sub 4} as a function of Na content. Two lifetime components are resolved. τ{sub 1} is attributed mainly to positron annihilation in the O-Co-O layers and shifts tomore » Na layers only in the H3 phase. The second lifetime τ{sub 2} is due to positron annihilation in vacancy clusters which may exist in the Na layers or grain boundary region. The size of vacancy clusters grow larger but their concentration decreases with increasing Na content in the range of 1.0 < x < 1.8. The thickness of O-Co-O layer also shows continuous increase with increasing Na content, which is reflected by the increase of τ{sub 1}. The thermal conductivity κ, on the other hand, shows systematic decrease with increasing Na content. This suggests that the increasing spacing of O-Co-O layer could effectively reduce the thermal conductivity of Na{sub x}Co{sub 2}O{sub 4}.« less

Globular Cluster Abundances from High-resolution, Integrated-light Spectroscopy. IV. The Large Magellanic Cloud: α, Fe-peak, Light, and Heavy Elements

NASA Astrophysics Data System (ADS)

Colucci, Janet E.; Bernstein, Rebecca A.; Cameron, Scott A.; McWilliam, Andrew

2012-02-01

We present detailed chemical abundances in eight clusters in the Large Magellanic Cloud (LMC). We measure abundances of 22 elements for clusters spanning a range in age of 0.05-12 Gyr, providing a comprehensive picture of the chemical enrichment and star formation history of the LMC. The abundances were obtained from individual absorption lines using a new method for analysis of high-resolution (R ~ 25,000), integrated-light (IL) spectra of star clusters. This method was developed and presented in Papers I, II, and III of this series. In this paper, we develop an additional IL χ2-minimization spectral synthesis technique to facilitate measurement of weak (~15 mÅ) spectral lines and abundances in low signal-to-noise ratio data (S/N ~ 30). Additionally, we supplement the IL abundance measurements with detailed abundances that we measure for individual stars in the youngest clusters (age < 2 Gyr) in our sample. In both the IL and stellar abundances we find evolution of [α/Fe] with [Fe/H] and age. Fe-peak abundance ratios are similar to those in the Milky Way (MW), with the exception of [Cu/Fe] and [Mn/Fe], which are sub-solar at high metallicities. The heavy elements Ba, La, Nd, Sm, and Eu are significantly enhanced in the youngest clusters. Also, the heavy to light s-process ratio is elevated relative to the MW ([Ba/Y] >+0.5) and increases with decreasing age, indicating a strong contribution of low-metallicity asymptotic giant branch star ejecta to the interstellar medium throughout the later history of the LMC. We also find a correlation of IL Na and Al abundances with cluster mass in the sense that more massive, older clusters are enriched in the light elements Na and Al with respect to Fe, which implies that these clusters harbor star-to-star abundance variations as is common in the MW. Lower mass, intermediate-age, and young clusters have Na and Al abundances that are lower and more consistent with LMC field stars. Our results can be used to constrain both future chemical evolution models for the LMC and theories of globular cluster formation. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Dehydration process in NaCl solutions under various external electric fields

NASA Astrophysics Data System (ADS)

Kadota, Kazunori; Shimosaka, Atsuko; Shirakawa, Yoshiyuki; Hidaka, Jusuke

2007-06-01

Ionic motions at solid-liquid interface in supersaturated NaCl solutions have been investigated by molecular dynamics (MD) simulation for understanding crystal growth processes. The density profile in the vicinity of the interfaces between NaCl(100) and the supersaturated NaCl solution was calculated. Diffusion coefficients of water molecules in the solution were estimated as a function of distance from the crystal interface. It turned out that the structure and dynamics of the solution in the interfaces was different from those of bulk solution owing to electric fields depending on the surface charge. Therefore, the electric field was applied to the supersaturated solutions and dehydration phenomenon occurring in the process of the crystal growth was discussed. As the electric field increased, it was observed that the Na+ keeping strongly hydration structure broke out by the electric force. In supersaturated concentration, the solution structure is significantly different from that of dilution and has a complicated structure with hydration ions and clusters of NaCl. If the electric fields were applied to the solutions, the breakout of hydration structure was not affected with increasing the supersaturated ratio. This reason is that the cluster structures are destroyed by the electric force. The situation depends on the electric field or crystal surface structure.

A Novel Feature Selection Technique for Text Classification Using Naïve Bayes.

PubMed

Dey Sarkar, Subhajit; Goswami, Saptarsi; Agarwal, Aman; Aktar, Javed

2014-01-01

With the proliferation of unstructured data, text classification or text categorization has found many applications in topic classification, sentiment analysis, authorship identification, spam detection, and so on. There are many classification algorithms available. Naïve Bayes remains one of the oldest and most popular classifiers. On one hand, implementation of naïve Bayes is simple and, on the other hand, this also requires fewer amounts of training data. From the literature review, it is found that naïve Bayes performs poorly compared to other classifiers in text classification. As a result, this makes the naïve Bayes classifier unusable in spite of the simplicity and intuitiveness of the model. In this paper, we propose a two-step feature selection method based on firstly a univariate feature selection and then feature clustering, where we use the univariate feature selection method to reduce the search space and then apply clustering to select relatively independent feature sets. We demonstrate the effectiveness of our method by a thorough evaluation and comparison over 13 datasets. The performance improvement thus achieved makes naïve Bayes comparable or superior to other classifiers. The proposed algorithm is shown to outperform other traditional methods like greedy search based wrapper or CFS.

A coupled-cluster study of photodetachment cross sections of closed-shell anions

NASA Astrophysics Data System (ADS)

Cukras, Janusz; Decleva, Piero; Coriani, Sonia

2014-11-01

We investigate the performance of Stieltjes Imaging applied to Lanczos pseudo-spectra generated at the coupled cluster singles and doubles, coupled cluster singles and approximate iterative doubles and coupled cluster singles levels of theory in modeling the photodetachment cross sections of the closed shell anions H-, Li-, Na-, F-, Cl-, and OH-. The accurate description of double excitations is found to play a much more important role than in the case of photoionization of neutral species.

A coupled-cluster study of photodetachment cross sections of closed-shell anions.

PubMed

Cukras, Janusz; Decleva, Piero; Coriani, Sonia

2014-11-07

We investigate the performance of Stieltjes Imaging applied to Lanczos pseudo-spectra generated at the coupled cluster singles and doubles, coupled cluster singles and approximate iterative doubles and coupled cluster singles levels of theory in modeling the photodetachment cross sections of the closed shell anions H(-), Li(-), Na(-), F(-), Cl(-), and OH(-). The accurate description of double excitations is found to play a much more important role than in the case of photoionization of neutral species.

A Versatile Low Temperature Synthetic Route to Zintl Phase Precursors: Na4Si4, Na4Ge4 and K4Ge4 as Examples

PubMed Central

Ma, Xuchu; Xu, Fen; Atkins, Tonya; Goforth, Andrea M.; Neiner, Doinita; Navrotsky, Alexandra; Kauzlarich, Susan M.

2010-01-01

Na4Si4 and Na4Ge4 are ideal chemical precursors for inorganic clathrate structures, clusters, and nanocrystals. The monoclinic Zintl phases, Na4Si4 and Na4Ge4, contain isolated homo-tetrahedranide [Si4]4− and [Ge4]4− clusters surrounded by alkali metal cations. In this study, a simple scalable route has been applied to prepare Zintl phases of composition Na4Si4 and Na4Ge4 using the reaction between NaH and Si or Ge at low temperature (420 °C for Na4Si4 and 270 °C for Na4Ge4). The method was also applied to K4Ge4, using KH and Ge as raw materials, to show the versatility of this approach. The influence of specific reaction conditions on the purity of these Zintl phases has been studied by controlling five factors: the method of reagent mixing (manual or ball milled), the stoichiometry between raw materials, the reaction temperature, the heating time and the gas flow rate. Moderate ball-milling and excess NaH or KH facilitate the formation of pure Na4Si4, Na4Ge4 or K4Ge4 at 420 °C (Na4Si4) or 270 °C (both M4Ge4 compounds, M = Na, K). TG/DSC analysis of the reaction of NaH and Ge indicates that ball milling reduces the temperature for reaction and confirms the formation temperature. This method provides large quantities of high quality Na4Si4 and Na4Ge4 without the need for specialized laboratory equipment, such as Schlenk lines, niobium/tantalum containers, or an arc welder, thereby expanding the accessibility and chemical utility of these phases by making them more convenient to prepare. This new synthetic method may also be extended to lithium-containing Zintl phases (LiH is commercially available) as well as to alkali metal-tetrel Zintl compounds of other compositions, e.g. K4Ge9. PMID:19921060

Self-assembled decanuclear Na(I)2Mn(II)4Mn(III)4 complexes: from discrete clusters to 1-D and 2-D structures, with the Mn(II)4Mn(III)4 unit displaying a large spin ground state and probable SMM behaviour.

PubMed

Langley, Stuart K; Chilton, Nicholas F; Moubaraki, Boujemaa; Murray, Keith S

2011-12-07

The synthesis, magnetic characterization and X-ray crystal structures are reported for five new manganese compounds, [Mn(III)(teaH(2))(sal)]·(1/2)H(2)O (1), [Na(I)(2)Mn(II)(4)Mn(III)(4)(teaH)(6)(sal)(4)(N(3))(2)(MeOH)(4)]·6MeOH (2), [Na(I)(2)Mn(II)(4)Mn(III)(4)(teaH)(6)(sal)(4)(N(3))(2)(MeOH)(2)](n)·7MeOH (3), [Na(I)(2)Mn(II)(4)Mn(III)(4)(teaH)(6)(sal)(4)(N(3))(2)(MeOH)(2)](n)·2MeOH·Et(2)O (4) and [K(I)(2)Mn(II)(4)Mn(III)(4)(teaH)(6)(sal)(4)(N(3))(2)(H(2)O)(2)](n)·5MeOH (5). Complex 1 is a mononuclear compound, formed via the reaction of Mn(NO(3))(2)·4H(2)O, triethanolamine (teaH(3)) and salicylic acid (salH(2)) in a basic methanolic solution. Compound 2 is a mixed-valent hetero-metallic cluster made up of a Mn(8)Na(2) decanuclear core and is formed via the reaction of sodium azide (NaN(3)) with 1. Compounds 3-5 are isolated as 1- or 2-D coordination polymers, each containing the decanuclear Mn(8)M(2) (M = Na(+) or K(+)) core building block as the repeating unit. Compound 3 is isolated when 1 is reacted with NaN(3) over a very short reaction time and forms a 1-D coordination polymer. Each unit displays inter-cluster bridges via the O-atoms of teaH(2-) ligands bonding to the sodium ions of an adjacent cluster. Increasing the reaction time appears to drive the formation of 4 which forms 2-D polymeric sheets and is a packing polymorph of 3. The addition of KMnO(4) and NaN(3) to 1 resulted in compound 5, which also forms a 1-D coordination polymer of the decanuclear core unit. The 1-D chains are now linked via inter-cluster potassium and salicylate bridges. Solid state DC susceptibility measurements were performed on compounds 1-5. The data for 1 are as expected for an S = 2 Mn(III) ion, with the isothermal M vs. H data being fitted by matrix diagonalization methods to give values of g and the axial (D) and rhombic (E) zero field splitting parameters of 2.02, -2.70 cm(-1) and 0.36 cm(-1) respectively. The data for 2-5, each with an identical Mn(II)(4)Mn(III)(4) metallic core, indicates large spin ground states, with likely values of S = 16 (±1) for each. Solid state AC susceptibility measurements confirm the large spin ground state values and is also suggestive of SMM behaviour for 2-5 as observed via the onset of frequency dependent out-of-phase peaks.

Dynamic behaviour of nanometre-sized defect clusters emitted from an atomic displacement cascade in Au at 50 K

NASA Astrophysics Data System (ADS)

Ono, K.; Miyamoto, M.; Arakawa, K.; Birtcher, R. C.

2017-09-01

We demonstrate the emission of nanometre-sized defect clusters from an isolated displacement cascade formed by irradiation of high-energy self-ions and their subsequent 1-D motion in Au at 50 K, using in situ electron microscopy. The small defect clusters emitted from a displacement cascade exhibited correlated back-and-forth 1-D motion along the [-1 1 0] direction and coalescence which results in their growth and reduction of their mobility. From the analysis of the random 1-D motion, the diffusivity of the small cluster was evaluated. Correlated 1-D motion and coalescence of clusters were understood via elastic interaction between small clusters. These results provide direct experimental evidence of the migration of small defect clusters and defect cascade evolution at low temperature.

The effect of disorder of small spheres on the photonic properties of the inverse binary NaCl-like structure

NASA Astrophysics Data System (ADS)

Pattabhiraman, Harini; Dijkstra, Marjolein

2017-09-01

Inverse opal structures are experimentally realisable photonic band gap materials. They suffer from the drawback of possessing band gaps that are extremely susceptible to structural disorders. A binary colloidal NaCl lattice, which is also experimentally realisable, is a promising alternative to these opals. In this work, we systematically analyse the effect of structural disorder of the small spheres on the photonic properties of an inverse binary NaCl lattice with a size ratio of 0.30 between the small and large spheres. The types of structural disorders studied include the position of the small spheres in the octahedral void of the large spheres, polydispersity in size of the small spheres, and the fraction of small spheres in the crystal. We find a low susceptibility of the band gap of the inverse NaCl lattice to the disorder of the small spheres.

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.

Accurate potential energy, dipole moment curves, and lifetimes of vibrational states of heteronuclear alkali dimers

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

Fedorov, Dmitry A.; Varganov, Sergey A., E-mail: svarganov@unr.edu; Derevianko, Andrei

2014-05-14

We calculate the potential energy curves, the permanent dipole moment curves, and the lifetimes of the ground and excited vibrational states of the heteronuclear alkali dimers XY (X, Y = Li, Na, K, Rb, Cs) in the X{sup 1}Σ{sup +} electronic state using the coupled cluster with singles doubles and triples method. All-electron quadruple-ζ basis sets with additional core functions are used for Li and Na, and small-core relativistic effective core potentials with quadruple-ζ quality basis sets are used for K, Rb, and Cs. The inclusion of the coupled cluster non-perturbative triple excitations is shown to be crucial for obtainingmore » the accurate potential energy curves. A large one-electron basis set with additional core functions is needed for the accurate prediction of permanent dipole moments. The dissociation energies are overestimated by only 14 cm{sup −1} for LiNa and by no more than 114 cm{sup −1} for the other molecules. The discrepancies between the experimental and calculated harmonic vibrational frequencies are less than 1.7 cm{sup −1}, and the discrepancies for the anharmonic correction are less than 0.1 cm{sup −1}. We show that correlation between atomic electronegativity differences and permanent dipole moment of heteronuclear alkali dimers is not perfect. To obtain the vibrational energies and wave functions the vibrational Schrödinger equation is solved with the B-spline basis set method. The transition dipole moments between all vibrational states, the Einstein coefficients, and the lifetimes of the vibrational states are calculated. We analyze the decay rates of the vibrational states in terms of spontaneous emission, and stimulated emission and absorption induced by black body radiation. In all studied heteronuclear alkali dimers the ground vibrational states have much longer lifetimes than any excited states.« less

Probing the atomic structure of metallic nanoclusters with the tip of a scanning tunneling microscope.

PubMed

Schouteden, Koen; Lauwaet, Koen; Janssens, Ewald; Barcaro, Giovanni; Fortunelli, Alessandro; Van Haesendonck, Chris; Lievens, Peter

2014-02-21

Preformed Co clusters with an average diameter of 2.5 nm are produced in the gas phase and are deposited under controlled ultra-high vacuum conditions onto a thin insulating NaCl film on Au(111). Relying on a combined experimental and theoretical investigation, we demonstrate visualization of the three-dimensional atomic structure of the Co clusters by high-resolution scanning tunneling microscopy (STM) using a Cl functionalized STM tip that can be obtained on the NaCl surface. More generally, use of a functionalized STM tip may allow for systematic atomic structure determination with STM of nanoparticles that are deposited on metal surfaces.

Nanostructured Ag-zeolite Composites as Luminescence-based Humidity Sensors.

PubMed

Coutino-Gonzalez, Eduardo; Baekelant, Wouter; Dieu, Bjorn; Roeffaers, Maarten B J; Hofkens, Johan

2016-11-15

Small silver clusters confined inside zeolite matrices have recently emerged as a novel type of highly luminescent materials. Their emission has high external quantum efficiencies (EQE) and spans the whole visible spectrum. It has been recently reported that the UV excited luminescence of partially Li-exchanged sodium Linde type A zeolites [LTA(Na)] containing luminescent silver clusters can be controlled by adjusting the water content of the zeolite. These samples showed a dynamic change in their emission color from blue to green and yellow upon an increase of the hydration level of the zeolite, showing the great potential that these materials can have as luminescence-based humidity sensors at the macro and micro scale. Here, we describe the detailed procedure to fabricate a humidity sensor prototype using silver-exchanged zeolite composites. The sensor is produced by suspending the luminescent Ag-zeolites in an aqueous solution of polyethylenimine (PEI) to subsequently deposit a film of the material onto a quartz plate. The coated plate is subjected to several hydration/dehydration cycles to show the functionality of the sensing film.

Nanostructured Ag-zeolite Composites as Luminescence-based Humidity Sensors

PubMed Central

Dieu, Bjorn; Roeffaers, Maarten B.J.; Hofkens, Johan

2016-01-01

Small silver clusters confined inside zeolite matrices have recently emerged as a novel type of highly luminescent materials. Their emission has high external quantum efficiencies (EQE) and spans the whole visible spectrum. It has been recently reported that the UV excited luminescence of partially Li-exchanged sodium Linde type A zeolites [LTA(Na)] containing luminescent silver clusters can be controlled by adjusting the water content of the zeolite. These samples showed a dynamic change in their emission color from blue to green and yellow upon an increase of the hydration level of the zeolite, showing the great potential that these materials can have as luminescence-based humidity sensors at the macro and micro scale. Here, we describe the detailed procedure to fabricate a humidity sensor prototype using silver-exchanged zeolite composites. The sensor is produced by suspending the luminescent Ag-zeolites in an aqueous solution of polyethylenimine (PEI) to subsequently deposit a film of the material onto a quartz plate. The coated plate is subjected to several hydration/dehydration cycles to show the functionality of the sensing film. PMID:27911397

Imaging nanoclusters in the constant height mode of the dynamic SFM.

PubMed

Barth, Clemens; Pakarinen, Olli H; Foster, Adam S; Henry, Claude R

2006-04-14

For the first time, high quality images of metal nanoclusters which were recorded in the constant height mode of a dynamic scanning force microscope (dynamic SFM) are shown. Surfaces of highly ordered pyrolytic graphite (HOPG) were used as a test substrate since metal nanoclusters with well defined and symmetric shapes can be created by epitaxial growth. We performed imaging of gold clusters with sizes between 5 and 15 nm in both scanning modes, constant Δf mode and constant height mode, and compared the image contrast. We notice that clusters in constant height images appear much sharper, and exhibit more reasonable lateral shapes and sizes in comparison to images recorded in the constant Δf mode. With the help of numerical simulations we show that only a microscopically small part of the tip apex (nanotip) is probably the main contributor for the image contrast formation. In principle, the constant height mode can be used for imaging surfaces of any material, e.g. ionic crystals, as shown for the system Au/NaCl(001).

The influence of ion hydration on nucleation and growth of LiF crystals in aqueous solution.

PubMed

Lanaro, G; Patey, G N

2018-01-14

Molecular dynamics (MD) simulations are employed to investigate crystal nucleation and growth in oversaturated aqueous LiF solutions. Results obtained for a range of temperatures provide evidence that the rate of crystal growth is determined by a substantial energy barrier (∼49 kJ mol -1 ) related to the loss of water from the ion hydration shells. Employing direct MD simulations, we do not observe spontaneous nucleation of LiF crystals at 300 K, but nucleation is easily observable in NVT simulations at 500 K. This contrasts with the NaCl case, where crystal nucleation is directly observed in similar simulations at 300 K. Based on these observations, together with a detailed analysis of ion clustering in metastable LiF solutions, we argue that the ion dehydration barrier also plays a key role in crystal nucleation. The hydration of the relatively small Li + and F - ions strongly influences the probability of forming large, crystal-like ion clusters, which are a necessary precursor to nucleation. This important factor is not accounted for in classical nucleation theory.

The influence of ion hydration on nucleation and growth of LiF crystals in aqueous solution

NASA Astrophysics Data System (ADS)

Lanaro, G.; Patey, G. N.

2018-01-01

Molecular dynamics (MD) simulations are employed to investigate crystal nucleation and growth in oversaturated aqueous LiF solutions. Results obtained for a range of temperatures provide evidence that the rate of crystal growth is determined by a substantial energy barrier (˜49 kJ mol-1) related to the loss of water from the ion hydration shells. Employing direct MD simulations, we do not observe spontaneous nucleation of LiF crystals at 300 K, but nucleation is easily observable in NVT simulations at 500 K. This contrasts with the NaCl case, where crystal nucleation is directly observed in similar simulations at 300 K. Based on these observations, together with a detailed analysis of ion clustering in metastable LiF solutions, we argue that the ion dehydration barrier also plays a key role in crystal nucleation. The hydration of the relatively small Li+ and F- ions strongly influences the probability of forming large, crystal-like ion clusters, which are a necessary precursor to nucleation. This important factor is not accounted for in classical nucleation theory.

Electronic structure, stability and magnetic properties of small M1-4(M = Fe, Co, Ni) clusters encapsulated inside a (BN)48 cage

NASA Astrophysics Data System (ADS)

Liang, Wenjuan; Jia, Jianfeng; Lv, Jin; Wu, Haishun

2015-02-01

The geometrical structure and magnetic properties of M1-4(M = Fe, Co and Ni) clusters within a (BN)48 cage were calculated at the BPW91/LanL2DZ level. The small M1-4 clusters generally prefer an off-centered position near the hexagonal rings in the (BN)48 cages. The (BN)48 cages can increase the stability of these small magnetic clusters while protecting the magnetic nature of M and M2 clusters.

A Chemical Composition Survey of the Iron-complex Globular Cluster NGC 6273 (M19)

NASA Astrophysics Data System (ADS)

Johnson, Christian I.; Caldwell, Nelson; Rich, R. Michael; Mateo, Mario; Bailey, John I., III; Clarkson, William I.; Olszewski, Edward W.; Walker, Matthew G.

2017-02-01

Recent observations have shown that a growing number of the most massive Galactic globular clusters contain multiple populations of stars with different [Fe/H] and neutron-capture element abundances. NGC 6273 has only recently been recognized as a member of this “iron-complex” cluster class, and we provide here a chemical and kinematic analysis of >300 red giant branch and asymptotic giant branch member stars using high-resolution spectra obtained with the Magellan-M2FS and VLT-FLAMES instruments. Multiple lines of evidence indicate that NGC 6273 possesses an intrinsic metallicity spread that ranges from about [Fe/H] = -2 to -1 dex, and may include at least three populations with different [Fe/H] values. The three populations identified here contain separate first (Na/Al-poor) and second (Na/Al-rich) generation stars, but a Mg-Al anti-correlation may only be present in stars with [Fe/H] ≳ -1.65. The strong correlation between [La/Eu] and [Fe/H] suggests that the s-process must have dominated the heavy element enrichment at higher metallicities. A small group of stars with low [α/Fe] is identified and may have been accreted from a former surrounding field star population. The cluster’s large abundance variations are coupled with a complex, extended, and multimodal blue horizontal branch (HB). The HB morphology and chemical abundances suggest that NGC 6273 may have an origin that is similar to ω Cen and M54. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program GO-14197. This paper includes data gathered with the 6.5 m Magellan Telescopes located as Las Campanas Observatory, Chile.

AGB subpopulations in the nearby globular cluster NGC 6397

NASA Astrophysics Data System (ADS)

MacLean, B. T.; Campbell, S. W.; De Silva, G. M.; Lattanzio, J.; D'Orazi, V.; Cottrell, P. L.; Momany, Y.; Casagrande, L.

2018-03-01

It has been well established that Galactic Globular clusters (GCs) harbour more than one stellar population, distinguishable by the anticorrelations of light-element abundances (C-N, Na-O, and Mg-Al). These studies have been extended recently to the asymptotic giant branch (AGB). Here, we investigate the AGB of NGC 6397 for the first time. We have performed an abundance analysis of high-resolution spectra of 47 red giant branch (RGB) and eight AGB stars, deriving Fe, Na, O, Mg, and Al abundances. We find that NGC 6397 shows no evidence of a deficit in Na-rich AGB stars, as reported for some other GCs - the subpopulation ratios of the AGB and RGB in NGC 6397 are identical, within uncertainties. This agrees with expectations from stellar theory. This GC acts as a control for our earlier work on the AGB of M4 (with contrasting results), since the same tools and methods were used.

α-synuclein assemblies sequester neuronal α3-Na+/K+-ATPase and impair Na+ gradient

PubMed Central

Shrivastava, Amulya Nidhi; Redeker, Virginie; Fritz, Nicolas; Pieri, Laura; Almeida, Leandro G; Spolidoro, Maria; Liebmann, Thomas; Bousset, Luc; Renner, Marianne; Léna, Clément; Aperia, Anita; Melki, Ronald; Triller, Antoine

2015-01-01

Extracellular α-synuclein (α-syn) assemblies can be up-taken by neurons; however, their interaction with the plasma membrane and proteins has not been studied specifically. Here we demonstrate that α-syn assemblies form clusters within the plasma membrane of neurons. Using a proteomic-based approach, we identify the α3-subunit of Na+/K+-ATPase (NKA) as a cell surface partner of α-syn assemblies. The interaction strength depended on the state of α-syn, fibrils being the strongest, oligomers weak, and monomers none. Mutations within the neuron-specific α3-subunit are linked to rapid-onset dystonia Parkinsonism (RDP) and alternating hemiplegia of childhood (AHC). We show that freely diffusing α3-NKA are trapped within α-syn clusters resulting in α3-NKA redistribution and formation of larger nanoclusters. This creates regions within the plasma membrane with reduced local densities of α3-NKA, thereby decreasing the efficiency of Na+ extrusion following stimulus. Thus, interactions of α3-NKA with extracellular α-syn assemblies reduce its pumping activity as its mutations in RDP/AHC. PMID:26323479

Effects of dilute aqueous NaCl solution on caffeine aggregation

NASA Astrophysics Data System (ADS)

Sharma, Bhanita; Paul, Sandip

2013-11-01

The effect of salt concentration on association properties of caffeine molecule was investigated by employing molecular dynamics simulations in isothermal-isobaric ensemble of eight caffeine molecules in pure water and three different salt (NaCl) concentrations, at 300 K temperature and 1 atm pressure. The concentration of caffeine was taken almost at the solubility limit. With increasing salt concentration, we observe enhancement of first peak height and appearance of a second peak in the caffeine-caffeine distribution function. Furthermore, our calculated solvent accessible area values and cluster structure analyses suggest formation of higher order caffeine cluster on addition of salt. The calculated hydrogen bond properties reveal that there is a modest decrease in the average number of water-caffeine hydrogen bonds on addition of NaCl salt. Also observed are: (i) decrease in probability of salt contact ion pair as well as decrease in the solvent separated ion pair formation with increasing salt concentration, (ii) a modest second shell collapse in the water structure, and (iii) dehydration of hydrophobic atomic sites of caffeine on addition of NaCl.

Effects of dilute aqueous NaCl solution on caffeine aggregation

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

Sharma, Bhanita; Paul, Sandip, E-mail: sandipp@iitg.ernet.in

The effect of salt concentration on association properties of caffeine molecule was investigated by employing molecular dynamics simulations in isothermal-isobaric ensemble of eight caffeine molecules in pure water and three different salt (NaCl) concentrations, at 300 K temperature and 1 atm pressure. The concentration of caffeine was taken almost at the solubility limit. With increasing salt concentration, we observe enhancement of first peak height and appearance of a second peak in the caffeine-caffeine distribution function. Furthermore, our calculated solvent accessible area values and cluster structure analyses suggest formation of higher order caffeine cluster on addition of salt. The calculated hydrogenmore » bond properties reveal that there is a modest decrease in the average number of water-caffeine hydrogen bonds on addition of NaCl salt. Also observed are: (i) decrease in probability of salt contact ion pair as well as decrease in the solvent separated ion pair formation with increasing salt concentration, (ii) a modest second shell collapse in the water structure, and (iii) dehydration of hydrophobic atomic sites of caffeine on addition of NaCl.« less

NORADRENERGIC INNERVATION OF THE RAT SPINAL CORD CAUDAL TO A COMPLETE SPINAL CORD TRANSECTION: EFFECTS OF OLFACTORY ENSHEATHING GLIA

PubMed Central

Takeoka, Aya; Kubasak, Marc D.; Zhong, Hui; Kaplan, Jennifer; Roy, Roland R.; Phelps, Patricia E.

2010-01-01

Transplantation of olfactory bulb-derived olfactory ensheathing glia (OEG) combined with step training improves hindlimb locomotion in adult rats with a complete spinal cord transection. Spinal cord injury studies use the presence of noradrenergic (NA) axons caudal to the injury site as evidence of axonal regeneration and we previously found more NA axons just caudal to the transection in OEG- than media-injected spinal rats. We therefore hypothesized that OEG transplantation promotes descending coeruleospinal regeneration that contributes to the recovery of hindlimb locomotion. Now we report that NA axons are present throughout the caudal stump of both media- and OEG-injected spinal rats and they enter the spinal cord from the periphery via dorsal and ventral roots and along large penetrating blood vessels. These results indicate that the presence of NA fibers in the caudal spinal cord is not a reliable indicator of coeruleospinal regeneration. We then asked if NA axons appose cholinergic neurons associated with motor functions, i.e., central canal cluster and partition cells (active during fictive locomotion) and somatic motor neurons (SMNs). We found more NA varicosities adjacent to central canal cluster cells, partition cells, and SMNs in the lumbar enlargement of OEG- than media-injected rats. As non-synaptic release of NA is common in the spinal cord, more associations between NA varicosities and motor-associated cholinergic neurons in the lumbar spinal cord may contribute to the improved treadmill stepping observed in OEG-injected spinal rats. This effect could be mediated through direct association with SMNs and/or indirectly via cholinergic interneurons. PMID:20025875

Small-scale Conformity of the Virgo Cluster Galaxies

NASA Astrophysics Data System (ADS)

Lee, Hye-Ran; Lee, Joon Hyeop; Jeong, Hyunjin; Park, Byeong-Gon

2016-06-01

We investigate the small-scale conformity in color between bright galaxies and their faint companions in the Virgo Cluster. Cluster member galaxies are spectroscopically determined using the Extended Virgo Cluster Catalog and the Sloan Digital Sky Survey Data Release 12. We find that the luminosity-weighted mean color of faint galaxies depends on the color of adjacent bright galaxy as well as on the cluster-scale environment (gravitational potential index). From this result for the entire area of the Virgo Cluster, it is not distinguishable whether the small-scale conformity is genuine or if it is artificially produced due to cluster-scale variation of galaxy color. To disentangle this degeneracy, we divide the Virgo Cluster area into three sub-areas so that the cluster-scale environmental dependence is minimized: A1 (central), A2 (intermediate), and A3 (outermost). We find conformity in color between bright galaxies and their faint companions (color-color slope significance S ˜ 2.73σ and correlation coefficient {cc}˜ 0.50) in A2, where the cluster-scale environmental dependence is almost negligible. On the other hand, the conformity is not significant or very marginal (S ˜ 1.75σ and {cc}˜ 0.27) in A1. The conformity is not significant either in A3 (S ˜ 1.59σ and {cc}˜ 0.44), but the sample size is too small in this area. These results are consistent with a scenario in which the small-scale conformity in a cluster is a vestige of infallen groups and these groups lose conformity as they come closer to the cluster center.

An anionic Na(i)-organic framework platform: separation of organic dyes and post-modification for highly sensitive detection of picric acid.

PubMed

Chen, Di-Ming; Tian, Jia-Yue; Wang, Zhuo-Wei; Liu, Chun-Sen; Chen, Min; Du, Miao

2017-09-26

A cage-based anionic Na(i)-organic framework with a unique Na 9 cluster-based secondary building unit and a cage-in-cage structure was constructed. The selective separation of dyes with different charges and sizes was investigated. Furthermore, the Rh6G@MOF composite could be applied as a recyclable fluorescent sensor for detecting picric acid (PA) with high sensitivity and selectivity.

Hydrothermal synthesis and photoluminescent properties of hierarchical GdPO4·H2O:Ln3+ (Ln3+ = Eu3+, Ce3+, Tb3+) flower-like clusters

NASA Astrophysics Data System (ADS)

Amurisana, Bao.; Zhiqiang, Song.; Haschaolu, O.; Yi, Chen; Tegus, O.

2018-02-01

3D hierarchical GdPO4·H2O:Ln3+ (Ln3+ = Eu3+, Ce3+, Tb3+) flower clusters were successfully prepared on glass slide substrate by a simple, economical hydrothermal process with the assistance of disodium ethylenediaminetetraacetic acid (Na2H2L, where L4- = (CH2COO)2N(CH2)2N(CH2COO)24-). In this process, Na2H2L was used as both a chelating agent and a structure-director. The hierarchical flower clusters have an average diameter of 7-12 μm and are composed of well-aligned microrods. The influence of the molar ratio of Na2H2L/Gd3+ and reaction time on the morphology was systematically studied. A possible crystal growth and formation mechanism of hierarchical flower clusters is proposed based on the evolution of morphology as a function of reaction time. The self-assembled GdPO4·H2O:Ln3+ superstructures exhibit strong orange-red (Eu3+, 5D0 → 7F1), green (Tb3+, 5D4 → 7F5) and near ultraviolet emissions (Ce3+, 5d → 7F5/2) under ultraviolet excitation, respectively. This study may provide a new channel for building hierarchically superstructued oxide micro/nanomaterials with optical and new properties.

Probing the early stages of salt nucleation—Experimental and theoretical investigations of sodium/potassium thiocyanate cluster anions

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

Deng, S. H. M.; Kong, Xiang-Yu; Wang, Xue-Bin, E-mail: xuebin.wang@pnnl.gov

2015-01-14

Due to the fast solvent evaporation in electrospray ionization (ESI), the concentration of initially dilute electrolyte solutions rapidly increases to afford the formation of supersaturated droplets and generation of various pristine anhydrous salt clusters in the gas phase. The size, composition, and charge distributions of these clusters, in principle, witness the nucleation evolution in solutions. Herein, we report a microscopic study on the initial stage of nucleation and crystallization of sodium/potassium thiocyanate salt solutions simulated in the ESI process. Singly charged M{sub x}(SCN){sub x+1}{sup −}, doubly charged M{sub y}(SCN){sub y+2}{sup 2−} (M = Na, K), and triply charged K{sub z}(SCN){submore » z+3}{sup 3−} anion clusters (x, y, and z stand for the number of alkali atoms in the singly, doubly, and triply charged clusters, respectively) were produced via electrospray of the corresponding salt solutions and were characterized by negative ion photoelectron spectroscopy (NIPES). The vertical detachment energies (VDEs) of these sodium/potassium thiocyanate cluster anions were obtained, and theoretical calculations were carried out for the sodium thiocyanate clusters in assisting spectral identification. The measured VDEs of singly charged anions M{sub x}(SCN){sub x+1}{sup −} (M = Na and K) demonstrate that they are superhalogen anions. The existence of doubly charged anions M{sub y}(SCN){sub y+2}{sup 2−} (y = 2x, x ≥ 4 and 3 for M = Na and K, respectively) and triply charged anions K{sub z}(SCN){sub z+3}{sup 3−} (z = 3x, x ≥ 6) was initially discovered from the photoelectron spectra for those singly charged anions of M{sub x}(SCN){sub x+1}{sup −} with the same mass-to-charge ratio (m/z), and later independently confirmed by the observation of their distinct mass spectral distributions and by taking their NIPE spectra for those pure multiply charged anions with their m/z different from the singly charged species. For large clusters, multiply charged clusters were found to become preferred, but at higher temperatures, those multiply charged clusters were suppressed. The series of anion clusters investigated here range from molecular-like M{sub 1}(SCN){sub 2}{sup −} to nano-sized K{sub 22}(SCN){sub 25}{sup 3−}, providing a vivid molecular-level growth pattern reflecting the initial salt nucleation process.« less

Synthesis and Molecular Structure of a Novel Compound Containing a Carbonate-Bridged Hexacalcium Cluster Cation Assembled on a Trimeric Trititanium(IV)-Substituted Wells-Dawson Polyoxometalate.

PubMed

Hoshino, Takahiro; Isobe, Rina; Kaneko, Takuya; Matsuki, Yusuke; Nomiya, Kenji

2017-08-21

A novel compound containing a hexacalcium cluster cation, one carbonate anion, and one calcium cation assembled on a trimeric trititanium(IV)-substituted Wells-Dawson polyoxometalate (POM), [{Ca 6 (CO 3 )(μ 3 -OH)(OH 2 ) 18 }(P 2 W 15 Ti 3 O 61 ) 3 Ca(OH 2 ) 3 ] 19- (Ca 7 Ti 9 Trimer), was obtained as the Na 7 Ca 6 salt (NaCa-Ca 7 Ti 9 Trimer) by the reaction of calcium chloride with the monomeric trititanium(IV)-substituted Wells-Dawson POM species "[P 2 W 15 Ti 3 O 59 (OH) 3 ] 9- " (Ti 3 Monomer). Ti 3 Monomer was generated in situ under basic conditions from the separately prepared tetrameric species with bridging Ti(OH 2 ) 3 groups and an encapsulated Cl - ion, [{P 2 W 15 Ti 3 O 59 (OH) 3 } 4 {μ 3 -Ti(H 2 O) 3 } 4 Cl] 21- (Ti 16 Tetramer). The Na 7 Ca 6 salt of Ca 7 Ti 9 Trimer was characterized by complete elemental analysis, thermogravimetric (TG) and differential thermal analyses (DTA), FTIR, single-crystal X-ray structure analysis, and solution 183 W and 31 P NMR spectroscopy. X-ray crystallography revealed that the [Ca 6 (CO 3 )(μ 3 -OH)(OH 2 ) 18 ] 9+ cluster cation was composed of six calcium cations linked by one μ 6 -carbonato anion and one μ 3 -OH - anion. The cluster cation was assembled, together with one calcium ion, on a trimeric species composed of three tri-Ti(IV)-substituted Wells-Dawson subunits linked by Ti-O-Ti bonds. Ca 7 Ti 9 Trimer is an unprecedented POM species containing an alkaline-earth-metal cluster cation and is the first example of alkaline-earth-metal ions clustered around a titanium(IV)-substituted POM.

Integrated light chemical tagging analyses of seven M31 outer halo globular clusters from the Pan-Andromeda Archaeological Survey

NASA Astrophysics Data System (ADS)

Sakari, Charli M.; Venn, Kim A.; Mackey, Dougal; Shetrone, Matthew D.; Dotter, Aaron; Ferguson, Annette M. N.; Huxor, Avon

2015-04-01

Detailed chemical abundances are presented for seven M31 outer halo globular clusters (with projected distances from M31 greater than 30 kpc), as derived from high-resolution integrated light spectra taken with the Hobby-Eberly Telescope. Five of these clusters were recently discovered in the Pan-Andromeda Archaeological Survey (PAndAS) - this paper presents the first determinations of integrated Fe, Na, Mg, Ca, Ti, Ni, Ba, and Eu abundances for these clusters. Four of the target clusters (PA06, PA53, PA54, and PA56) are metal poor ([Fe/H] < -1.5), α-enhanced (though they are possibly less α-enhanced than Milky Way stars at the 1σ level), and show signs of star-to-star Na and Mg variations. The other three globular clusters (H10, H23, and PA17) are more metal rich, with metallicities ranging from [Fe/H] = -1.4 to -0.9. While H23 is chemically similar to Milky Way field stars, Milky Way globular clusters, and other M31 clusters, H10 and PA17, have moderately low [Ca/Fe], compared to Milky Way field stars and clusters. Additionally, PA17's high [Mg/Ca] and [Ba/Eu] ratios are distinct from Milky Way stars, and are in better agreement with the stars and clusters in the Large Magellanic Cloud. None of the clusters studied here can be conclusively linked to any of the identified streams from PAndAS; however, based on their locations, kinematics, metallicities, and detailed abundances, the most metal-rich PAndAS clusters H23 and PA17 may be associated with the progenitor of the Giant Stellar Stream, H10 may be associated with the SW cloud, and PA53 and PA56 may be associated with the eastern cloud.

Quantifying substructures in Hubble Frontier Field clusters: comparison with ΛCDM simulations

DOE PAGES

Mohammed, Irshad; Saha, Prasenjit; Williams, Liliya L. R.; ...

2016-04-13

The Hubble Frontier Fields (HFF) are six clusters of galaxies, all showing indications of recent mergers, which have recently been observed for lensed images. As such they are the natural laboratories to study the merging history of galaxy clusters. In this work, we explore the 2D power spectrum of the mass distributionmore » $$P_{\\rm M}(k)$$ as a measure of substructure. We compare $$P_{\\rm M}(k)$$ of these clusters (obtained using strong gravitational lensing) to that of $$\\Lambda$$CDM simulated clusters of similar mass. In order to compute lensing $$P_{\\rm M}(k)$$, we produced free-form lensing mass reconstructions of HFF clusters, without any light traces mass (LTM) assumption. Moreover, the inferred power at small scales tends to be larger if (i)~the cluster is at lower redshift, and/or (ii)~there are deeper observations and hence more lensed images. In contrast, lens reconstructions assuming LTM show higher power at small scales even with fewer lensed images; it appears the small scale power in the LTM reconstructions is dominated by light information, rather than the lensing data. The average lensing derived $$P_{\\rm M}(k)$$ shows lower power at small scales as compared to that of simulated clusters at redshift zero, both dark-matter only and hydrodynamical. The possible reasons are: (i)~the available strong lensing data are limited in their effective spatial resolution on the mass distribution, (ii)~HFF clusters have yet to build the small scale power they would have at $$z\\sim 0$$, or (iii)~simulations are somehow overestimating the small scale power.« less

Glucose Transport into Everted Sacs of the Small Intestine of Mice

ERIC Educational Resources Information Center

Hamilton, Kirk L.; Butt, A. Grant

2013-01-01

The Na[superscript +]-glucose cotransporter is a key transport protein that is responsible for absorbing Na[superscript +] and glucose from the luminal contents of the small intestine and reabsorption by the proximal straight tubule of the nephron. Robert K. Crane originally described the cellular model of absorption of Na[superscript +] and…

Resolving the problem of galaxy clustering on small scales: any new physics needed?

NASA Astrophysics Data System (ADS)

Kang, X.

2014-02-01

Galaxy clustering sets strong constraints on the physics governing galaxy formation and evolution. However, most current models fail to reproduce the clustering of low-mass galaxies on small scales (r < 1 Mpc h-1). In this paper, we study the galaxy clusterings predicted from a few semi-analytical models. We first compare two Munich versions, Guo et al. and De Lucia & Blaizot. The Guo11 model well reproduces the galaxy stellar mass function, but overpredicts the clustering of low-mass galaxies on small scales. The DLB07 model provides a better fit to the clustering on small scales, but overpredicts the stellar mass function. These seem to be puzzling. The clustering on small scales is dominated by galaxies in the same dark matter halo, and there is slightly more fraction of satellite galaxies residing in massive haloes in the Guo11 model, which is the dominant contribution to the clustering discrepancy between the two models. However, both models still overpredict the clustering at 0.1 < r < 10 Mpc h-1 for low-mass galaxies. This is because both models overpredict the number of satellites by 30 per cent in massive haloes than the data. We show that the Guo11 model could be slightly modified to simultaneously fit the stellar mass function and clusterings, but that cannot be easily achieved in the DLB07 model. The better agreement of DLB07 model with the data actually comes as a coincidence as it predicts too many low-mass central galaxies which are less clustered and thus brings down the total clustering. Finally, we show the predictions from the semi-analytical models of Kang et al. We find that this model can simultaneously fit the stellar mass function and galaxy clustering if the supernova feedback in satellite galaxies is stronger. We conclude that semi-analytical models are now able to solve the small-scales clustering problem, without invoking of any other new physics or changing the dark matter properties, such as the recent favoured warm dark matter.

A DIM model for sodium cluster-ions interacting with a charged conducting sphere

NASA Astrophysics Data System (ADS)

Kuntz, P. J.

A diatomics-in-molecules (DIM) model for the energy, shape and charge distribution of metal cluster ions in the presence of a charged insulated conducting sphere is presented. The electrostatic interaction between the sphere and the cluster-ion is introduced in a self-consistent manner which allows the sphere to be polarized by the ion and the ion by the sphere. This interaction appears in the diagonal elements of the model Hamiltonian matrix in such a way that the lowest eigenvalue includes the correct electrostatic energy for the charge distribution in the ground state. The model is applied to the calculation of fusion barriers for Na+2 and Na+3 ions. When both the charge distribution and the geometric configuration of the cluster-ion are allowed to relax freely, the energy as a function of distance from the sphere is nearly the same as that calculated from the electrostatic energy alone, which implies that details of the molecular structure of the cluster-ion can be neglected in calculating fusion barriers from charge polarization alone. That the fusion barriers lie sufficiently far away from the sphere so that the molecule does not dissociate under the influence of the Coulomb interaction confirms that it is meaningful to speak of two separate entities at the barrier position.

Improving Spectral Image Classification through Band-Ratio Optimization and Pixel Clustering

NASA Astrophysics Data System (ADS)

O'Neill, M.; Burt, C.; McKenna, I.; Kimblin, C.

2017-12-01

The Underground Nuclear Explosion Signatures Experiment (UNESE) seeks to characterize non-prompt observables from underground nuclear explosions (UNE). As part of this effort, we evaluated the ability of DigitalGlobe's WorldView-3 (WV3) to detect and map UNE signatures. WV3 is the current state-of-the-art, commercial, multispectral imaging satellite; however, it has relatively limited spectral and spatial resolutions. These limitations impede image classifiers from detecting targets that are spatially small and lack distinct spectral features. In order to improve classification results, we developed custom algorithms to reduce false positive rates while increasing true positive rates via a band-ratio optimization and pixel clustering front-end. The clusters resulting from these algorithms were processed with standard spectral image classifiers such as Mixture-Tuned Matched Filter (MTMF) and Adaptive Coherence Estimator (ACE). WV3 and AVIRIS data of Cuprite, Nevada, were used as a validation data set. These data were processed with a standard classification approach using MTMF and ACE algorithms. They were also processed using the custom front-end prior to the standard approach. A comparison of the results shows that the custom front-end significantly increases the true positive rate and decreases the false positive rate.This work was done by National Security Technologies, LLC, under Contract No. DE-AC52-06NA25946 with the U.S. Department of Energy. DOE/NV/25946-3283.

Diverse functions of miR-17-92 cluster microRNAs in T helper cells.

PubMed

Baumjohann, Dirk

2018-06-01

T helper (Th) cells are critically involved in adaptive immune responses against various pathogens. In contrast, dysregulated T helper cell responses are associated with a variety of diseases, including autoimmunity, allergies, and cancer. Differentiation of naïve CD4 + T cells into effector T helper cell subsets, including Th1, Th2, Th17, Treg, and T follicular helper (Tfh), requires precise dosing of signaling molecules and transcription factors. MicroRNAs (miRNAs), which are small endogenously expressed RNAs that regulate gene expression, play important roles in these processes. The miR-17-92 cluster, a miRNA polycistron also known as oncomiR-1, has emerged as a central integrator of gene expression events that govern T helper cell differentiation pathways. The complexity of miR-17-92-mediated gene regulation lies in the nature of this miRNA cluster, which consists of six different miRNAs. Individual miR-17-92 miRNAs, albeit initially transcribed as one transcript, can have cooperative or opposing effects on biological processes. Therefore, a better understanding of the molecular regulation of miR-17-92 and its downstream networks will provide important insights into T helper cell differentiation and diversity that may be harnessed for the design of advanced T cell-targeting therapies. Copyright © 2018 Elsevier B.V. All rights reserved.

CHEMICAL ABUNDANCES OF MEMBER STARS IN THE OPEN CLUSTER NGC 2632 (PRAESEPE)

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

Yang, X. L.; Chen, Y. Q.; Zhao, G.

2015-11-15

Based on high-resolution, high signal-to-noise ratio spectra, we present abundances of 17 elements (Fe, O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Co, Ni, Y, Zr, Ba, La) for six stars (one Am star, one F dwarf star, and four GK giant stars) and radial velocities for 18 proper-motion selected member stars in the open cluster NGC 2632. In the Am star, s-process elements Y and Ba are clearly overabundant, which may be considered as an indicator of a peculiar Am star. The average [Fe/H] is 0.16 ± 0.06 from four GK giant member stars, which is similarmore » to that of solar-type stars in the literature. As compared with dwarf stars, significant overabundances are found for Na, Mg, and Ba elements in our giant stars, which can be explained by the evolutionary effect. We also detect a star-to-star scatter of [Na/Fe] ratios among four giants which locate approximately at the same position in the CMD. Finally, we perform an analysis on the possible connection between the abundance and spatial structure of NGC 2632, but we find no inhomogeneous abundance among different clumps of stars in this cluster based on our limited sample.« less

Noradrenergic innervation of the rat spinal cord caudal to a complete spinal cord transection: effects of olfactory ensheathing glia.

PubMed

Takeoka, Aya; Kubasak, Marc D; Zhong, Hui; Kaplan, Jennifer; Roy, Roland R; Phelps, Patricia E

2010-03-01

Transplantation of olfactory bulb-derived olfactory ensheathing glia (OEG) combined with step training improves hindlimb locomotion in adult rats with a complete spinal cord transection. Spinal cord injury studies use the presence of noradrenergic (NA) axons caudal to the injury site as evidence of axonal regeneration and we previously found more NA axons just caudal to the transection in OEG- than media-injected spinal rats. We therefore hypothesized that OEG transplantation promotes descending coeruleospinal regeneration that contributes to the recovery of hindlimb locomotion. Now we report that NA axons are present throughout the caudal stump of both media- and OEG-injected spinal rats and they enter the spinal cord from the periphery via dorsal and ventral roots and along large penetrating blood vessels. These results indicate that the presence of NA fibers in the caudal spinal cord is not a reliable indicator of coeruleospinal regeneration. We then asked if NA axons appose cholinergic neurons associated with motor functions, i.e., central canal cluster and partition cells (active during fictive locomotion) and somatic motor neurons (SMNs). We found more NA varicosities adjacent to central canal cluster cells, partition cells, and SMNs in the lumbar enlargement of OEG- than media-injected rats. As non-synaptic release of NA is common in the spinal cord, more associations between NA varicosities and motor-associated cholinergic neurons in the lumbar spinal cord may contribute to the improved treadmill stepping observed in OEG-injected spinal rats. This effect could be mediated through direct association with SMNs and/or indirectly via cholinergic interneurons. Copyright 2009 Elsevier Inc. All rights reserved.

The VLT-FLAMES Tarantula Survey. IX. The interstellar medium seen through diffuse interstellar bands and neutral sodium&

NASA Astrophysics Data System (ADS)

van Loon, J. Th.; Bailey, M.; Tatton, B. L.; Maíz Apellániz, J.; Crowther, P. A.; de Koter, A.; Evans, C. J.; Hénault-Brunet, V.; Howarth, I. D.; Richter, P.; Sana, H.; Simón-Díaz, S.; Taylor, W.; Walborn, N. R.

2013-02-01

Context. The Tarantula Nebula (a.k.a. 30 Dor) is a spectacular star-forming region in the Large Magellanic Cloud (LMC), seen through gas in the Galactic disc and halo. Diffuse interstellar bands (DIBs) offer a unique probe of the diffuse, cool-warm gas in these regions. Aims: The aim is to use DIBs as diagnostics of the local interstellar conditions, whilst at the same time deriving properties of the yet-unknown carriers of these enigmatic spectral features. Methods: Spectra of over 800 early-type stars from the Very Large Telescope Flames Tarantula Survey (VFTS) were analysed. Maps were created, separately, for the Galactic and LMC absorption in the DIBs at 4428 and 6614 Å and - in a smaller region near the central cluster R 136 - neutral sodium (the Na i D doublet); we also measured the DIBs at 5780 and 5797 Å. Results: The maps show strong 4428 and 6614 Å DIBs in the quiescent cloud complex to the south of 30 Dor but weak absorption in the harsher environments to the north (bubbles) and near the OB associations. The Na maps show at least five kinematic components in the LMC and a shell-like structure surrounding R 136, and small-scale structure in the Milky Way. The strengths of the 4428, 5780, 5797 and 6614 Å DIBs are correlated, also with Na absorption and visual extinction. The strong 4428 Å DIB is present already at low Na column density but the 6614, 5780 and 5797 Å DIBs start to be detectable at subsequently larger Na column densities. Conclusions: The carriers of the 4428, 6614, 5780 and 5797 Å DIBs are increasingly prone to removal from irradiated gas. The relative strength of the 5780 and 5797 Å DIBs clearly confirm the Tarantula Nebula as well as Galactic high-latitude gas to represent a harsh radiation environment. The resilience of the 4428 Å DIB suggests its carrier is large, compact and neutral. Structure is detected in the distribution of cool-warm gas on scales between one and >100 pc in the LMC and as little as 0.01 pc in the Sun's vicinity. Stellar winds from the central cluster R 136 have created an expanding shell; some infalling gas is also detected, reminiscent of a galactic "fountain". Full Tables A.2-A.4 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/550/A108

Identification and Phylogenetic Analysis of Tityus pachyurus and Tityus obscurus Novel Putative Na+-Channel Scorpion Toxins

PubMed Central

Guerrero-Vargas, Jimmy A.; Mourão, Caroline B. F.; Quintero-Hernández, Verónica; Possani, Lourival D.; Schwartz, Elisabeth F.

2012-01-01

Background Colombia and Brazil are affected by severe cases of scorpionism. In Colombia the most dangerous accidents are caused by Tityus pachyurus that is widely distributed around this country. In the Brazilian Amazonian region scorpion stings are a common event caused by Tityus obscurus. The main objective of this work was to perform the molecular cloning of the putative Na+-channel scorpion toxins (NaScTxs) from T. pachyurus and T. obscurus venom glands and to analyze their phylogenetic relationship with other known NaScTxs from Tityus species. Methodology/Principal Findings cDNA libraries from venom glands of these two species were constructed and five nucleotide sequences from T. pachyurus were identified as putative modulators of Na+-channels, and were named Tpa4, Tpa5, Tpa6, Tpa7 and Tpa8; the latter being the first anti-insect excitatory β-class NaScTx in Tityus scorpion venom to be described. Fifteen sequences from T. obscurus were identified as putative NaScTxs, among which three had been previously described, and the others were named To4 to To15. The peptides Tpa4, Tpa5, Tpa6, To6, To7, To9, To10 and To14 are closely related to the α-class NaScTxs, whereas Tpa7, Tpa8, To4, To8, To12 and To15 sequences are more related to the β-class NaScTxs. To5 is possibly an arthropod specific toxin. To11 and To13 share sequence similarities with both α and β NaScTxs. By means of phylogenetic analysis using the Maximum Parsimony method and the known NaScTxs from Tityus species, these toxins were clustered into 14 distinct groups. Conclusions/Significance This communication describes new putative NaScTxs from T. pachyurus and T. obscurus and their phylogenetic analysis. The results indicate clear geographic separation between scorpions of Tityus genus inhabiting the Amazonian and Mountain Andes regions and those distributed over the Southern of the Amazonian rainforest. Based on the consensus sequences for the different clusters, a new nomenclature for the NaScTxs is proposed. PMID:22355312

Chemodynamical Clustering Applied to APOGEE Data: Rediscovering Globular Clusters

NASA Astrophysics Data System (ADS)

Chen, Boquan; D’Onghia, Elena; Pardy, Stephen A.; Pasquali, Anna; Bertelli Motta, Clio; Hanlon, Bret; Grebel, Eva K.

2018-06-01

We have developed a novel technique based on a clustering algorithm that searches for kinematically and chemically clustered stars in the APOGEE DR12 Cannon data. As compared to classical chemical tagging, the kinematic information included in our methodology allows us to identify stars that are members of known globular clusters with greater confidence. We apply our algorithm to the entire APOGEE catalog of 150,615 stars whose chemical abundances are derived by the Cannon. Our methodology found anticorrelations between the elements Al and Mg, Na and O, and C and N previously identified in the optical spectra in globular clusters, even though we omit these elements in our algorithm. Our algorithm identifies globular clusters without a priori knowledge of their locations in the sky. Thus, not only does this technique promise to discover new globular clusters, but it also allows us to identify candidate streams of kinematically and chemically clustered stars in the Milky Way.

Dynamic free energy surfaces for sodium diffusion in type II silicon clathrates.

PubMed

Slingsby, J G; Rorrer, N A; Krishna, L; Toberer, E S; Koh, C A; Maupin, C M

2016-02-21

Earth abundant semiconducting type II Si clathrates have attracted attention as photovoltaic materials due to their wide band gaps. To realize the semiconducting properties of these materials, guest species that arise during the synthesis process must be completely evacuated from the host cage structure post synthesis. A common guest species utilized in the synthesis of Si clathrates is Na (metal), which templates the clathrate cage formation. Previous experimental investigations have identified that it is possible to evacuate Na from type II clathrates to an occupancy of less than 1 Na per unit cell. This work investigates the energetics, kinetics, and resulting mechanism of Na diffusion through type II Si clathrates by means of biased molecular dynamics and kinetic Monte Carlo simulations. Well-tempered metadynamics has been used to determine the potential of mean force for Na moving between clathrate cages, from which the thermodynamic preferences and transition barrier heights have been obtained. Kinetic Monte Carlo simulations based on the metadynamics results have identified the mechanism of Na diffusion in type II Si clathrates. The overall mechanism consists of a coupled diffusive process linked via electrostatic guest-guest interactions. The large occupied hexakaidechedral cages initially empty their Na guests to adjacent empty large cages, thereby changing the local electrostatic environment around the occupied small pentagonal dodecahedral cages and increasing the probability of Na guests to leave the small cages. This coupled process continues through the cross-over point that is identified as the point where large and small cages are equally occupied by Na guests. Further Na removal results in the majority of guests residing in the large cages as opposed to the small cages, in agreement with experiments, and ultimately a Na free structure.

Time dependent density functional calculation of plasmon response in clusters

NASA Astrophysics Data System (ADS)

Wang, Feng; Zhang, Feng-Shou; Eric, Suraud

2003-02-01

We have introduced a theoretical scheme for the efficient description of the optical response of a cluster based on the time-dependent density functional theory. The practical implementation is done by means of the fully fledged time-dependent local density approximation scheme, which is solved directly in the time domain without any linearization. As an example we consider the simple Na2 cluster and compute its surface plasmon photoabsorption cross section, which is in good agreement with the experiments.

Differences in the rotational properties of multiple stellar populations in M13: a faster rotation for the `extreme' chemical subpopulation

NASA Astrophysics Data System (ADS)

Cordero, M. J.; Hénault-Brunet, V.; Pilachowski, C. A.; Balbinot, E.; Johnson, C. I.; Varri, A. L.

2017-03-01

We use radial velocities from spectra of giants obtained with the WIYN telescope, coupled with existing chemical abundance measurements of Na and O for the same stars, to probe the presence of kinematic differences among the multiple populations of the globular cluster (GC) M13. To characterize the kinematics of various chemical subsamples, we introduce a method using Bayesian inference along with a Markov chain Monte Carlo algorithm to fit a six-parameter kinematic model (including rotation) to these subsamples. We find that the so-called extreme population (Na-enhanced and extremely O-depleted) exhibits faster rotation around the centre of the cluster than the other cluster stars, in particular, when compared with the dominant `intermediate' population (moderately Na-enhanced and O-depleted). The most likely difference between the rotational amplitude of this extreme population and that of the intermediate population is found to be ˜4 km s-1 , with a 98.4 per cent probability that the rotational amplitude of the extreme population is larger than that of the intermediate population. We argue that the observed difference in rotational amplitudes, obtained when splitting subsamples according to their chemistry, is not a product of the long-term dynamical evolution of the cluster, but more likely a surviving feature imprinted early in the formation history of this GC and its multiple populations. We also find an agreement (within uncertainties) in the inferred position angle of the rotation axis of the different subpopulations considered. We discuss the constraints that these results may place on various formation scenarios.

Generation and collision-induced dissociation of ammonium tetrafluoroborate cluster ions.

PubMed

Dain, Ryan P; Van Stipdonk, Michael J

2008-07-01

Singly and doubly charged cluster ions of ammonium tetrafluoroborate (NH4BF4) with general formula [(NH4BF4)nNH4]+ and [(NH4BF4)m(NH4)2]2+, respectively, were generated by electrospray ionization (ESI) and their fragmentation examined using collision-induced dissociation (CID) and ion-trap tandem mass spectrometry. CID of [(NH4BF4)nNH4]+ caused the loss of one or more neutral NH4BF4 units. The n = 2 cluster, [(NH4BF4)2NH4]+, was unique in that it also exhibited a dissociation pathway in which HBF4 was eliminated to create [(NH4BF4)(NH3)NH4]+. Dissociation of [(NH4BF4)m(NH4)2]2+ occurred through two general pathways: (a) 'fission' to produce singly charged cluster ions and (b) elimination of one or more neutral NH4BF4 units to leave doubly charged product ions. CID profiles, and measurements of changing precursor and product ion signal intensity as a function of applied collision voltage, were collected for [(NH4BF4)nNH4]+ and compared with those for analogous [(NaBF4)nNa]+ and [(KBF4)nK]+ ions to determine the influence of the cation on the relative stability of cluster ions. In general, the [(NH4BF4)nNH4]+ clusters were found to be easier to dissociate than both the sodium and potassium clusters of comparable size, with [(KBF4)nK]+ ions the most difficult to dissociate.

Rational synthesis of high nuclearity Mo/Fe/S clusters: the reductive coupling approach in the convenient synthesis of (Cl(4)-cat)(2)Mo(2)Fe(6)S(8)(PR(3))(6) [R = Et, (n)Pr, (n)Bu] and the new [(Cl(4)-cat)(2)Mo(2)Fe(2)S(3)O(PEt(3))(3)Cl]-1/2(Fe(PEt(3))(2)(MeCN)(4)) and (Cl(4)-cat)(2)Mo(2)Fe(3)S(5)(PEt(3))(5) clusters.

PubMed

Han, J; Koutmos, M; Ahmad, S A; Coucouvanis, D

2001-11-05

A general method for the synthesis of high nuclearity Mo/Fe/S clusters is presented and involves the reductive coupling of the (Et(4)N)(2)[(Cl(4)-cat)MoOFeS(2)Cl(2)] (I) and (Et(4)N)(2)[Fe(2)S(2)Cl(4)] (II) clusters. The reaction of I and II with Fe(PR(3))(2)Cl(2) or sodium salts of noncoordinating anions such as NaPF(6) or NaBPh(4) in the presence of PR(3) (R = Et, (n)Pr, or (n)Bu) affords (Cl(4)-cat)(2)Mo(2)Fe(6)S(8)(PR(3))(6) [R = Et (IIIa), (n)Pr (IIIb), (n)Bu (IIIc)], Fe(6)S(6)(PEt(3))(4)Cl(2) (IV) and (PF(6))[Fe(6)S(8)(P(n)Pr(3))(6)] (V) as byproducts. The isolation of (Et(4)N)[Fe(PEt(3))Cl(3)] (VI), NaCl, and SPEt(3) supports a reductive coupling mechanism. Cluster IV and V also have been synthesized by the reductive self-coupling of compound II. The reductive coupling reaction between I and II by PEt(3) and NaPF(6) in a 1:1 ratio produces the (Et(4)N)(2)[(Cl(4)-cat)Mo(L)Fe(3)S(4)Cl(3)] clusters [L = MeCN (VIIa), THF (VIIb)]. The hitherto unknown [(Cl(4)-cat)(2)Mo(2)Fe(2)S(3)O(PEt(3))(3)Cl](+) cluster (VIII) has been isolated as the 2:1 salt of the (Fe(PEt(3))(2)(MeCN)(4))(2+) cation after the reductive self-coupling reaction of I in the presence of Fe(PEt(3))(2)Cl(2). Cluster VIII crystallizes in the monoclinic space group P2(1)/c with a = 11.098(3) A, b = 22.827(6) A, c = 25.855(6) A, beta = 91.680(4) degrees, and Z = 4. The formal oxidation states of metal atoms in VIII have been assigned as Mo(III), Mo(IV), Fe(II), and Fe(III) on the basis of zero-field Mössbauer spectra. The Fe(PEt(3))(2)(MeCN)(4) cation of VIII is also synthesized independently, isolated as the BPh(4)(-) salt (IX), and has been structurally characterized. The reductive coupling of compound I also affords in low yield the new (Cl(4)-cat)(2)Mo(2)Fe(3)S(5)(PEt(3))(5) cluster (X) as a byproduct. Cluster X crystallizes in the monoclinic space group P2(1)/n with a = 14.811(3) A, b = 22.188(4) A, c = 21.864(4) A, beta = 100.124(3) degrees, and Z = 4 and the structure shows very short Mo-Fe, Fe-Fe, Mo-S, Fe-S bonds. The oxidation states of the metal atoms in this neutral cluster (X) have been assigned as Mo(IV)Mo(III)Fe(II)Fe(II)Fe(III) based on zero-field Mössbauer and magnetic measurement. All Fe atoms are high spin and two of the three Fe-Fe distances are found at 2.4683(9) A and 2.4721(9) A.

High-performance radiofrequency coils for (23)Na MRI: brain and musculoskeletal applications.

PubMed

Wiggins, Graham C; Brown, Ryan; Lakshmanan, Karthik

2016-02-01

(23)Na RF coil design for brain and MSK applications presents a number of challenges, including poor coil loading for arrays of small coils and SNR penalties associated with providing (1)H capability with the same coil. The basics of RF coil design are described, as well as a review of historical approaches to dual tuning. There follows a review of published high performance coil designs for MSK and brain imaging. Several coil designs have been demonstrated at 7T and 3T which incorporate close-fitting receive arrays and in some cases design features which provide (1)H imaging with little penalty to (23)Na sensitivity. The "nested coplanar loop" approach is examined, in which small transmit-receive (1)H elements are placed within each (23)Na loop, presenting only a small perturbation to (23)Na performance and minimizing RF shielding issues. Other designs incorporating transmit-receive arrays for (23)Na and (1)H are discussed including a 9.4 T (23)Na/(1)H brain coil. Great gains in (23)Na SNR have been made with many of these designs, but simultaneously achieving high performance for 1H remains elusive. Copyright © 2015 John Wiley & Sons, Ltd.

Atom-Level Understanding of the Sodiation Process in Silicon Anode Material.

PubMed

Jung, Sung Chul; Jung, Dae Soo; Choi, Jang Wook; Han, Young-Kyu

2014-04-03

Despite the exceptionally large capacities in Li ion batteries, Si has been considered inappropriate for applications in Na ion batteries. We report an atomic-level study on the applicability of a Si anode in Na ion batteries using ab initio molecular dynamics simulations. While crystalline Si is not suitable for alloying with Na atoms, amorphous Si can accommodate 0.76 Na atoms per Si atom, corresponding to a specific capacity of 725 mA h g(-1). Bader charge analyses reveal that the sodiation of an amorphous Si electrode continues until before the local Na-rich clusters containing neutral Na atoms are formed. The amorphous Na0.76Si phase undergoes a volume expansion of 114% and shows a Na diffusivity of 7 × 10(-10) cm(2) s(-1) at room temperature. Overall, the amorphous Si phase turns out quite attractive in performance compared to other alloy-type anode materials. This work suggests that amorphous Si might be a competitive candidate for Na ion battery anodes.

High energy conformers of M(+)(APE)(H2O)(0-1)Ar(0-1) clusters revealed by combined IR-PD and DFT-MD anharmonic vibrational spectroscopy.

PubMed

Brites, V; Nicely, A L; Sieffert, N; Gaigeot, M-P; Lisy, J M

2014-07-14

IR-PD vibrational spectroscopy and DFT-based molecular dynamics simulations are combined in order to unravel the structures of M(+)(APE)(H2O)0-1 ionic clusters (M = Na, K), where APE (2-amino-1-phenyl ethanol) is commonly used as an analogue for the noradrenaline neurotransmitter. The strength of the synergy between experiments and simulations presented here is that DFT-MD provides anharmonic vibrational spectra that unambiguously help assign the ionic clusters structures. Depending on the interacting cation, we have found that the lowest energy conformers of K(+)(APE)(H2O)0-1 clusters are formed, while the lowest energy conformers of Na(+)(APE)(H2O)0-1 clusters can only be observed through water loss channel (i.e. without argon tagged to the clusters). Trapping of higher energy conformers is observed when the argon loss channel is recorded in the experiment. This has been rationalized by transition state energies. The dynamical anharmonic vibrational spectra unambiguously provide the prominent OH stretch due to the OH···NH2 H-bond, within 10 cm(-1) of the experiment, hence reproducing the 240-300 cm(-1) red-shift (depending on the interacting cation) from bare neutral APE. When this H-bond is not present, the dynamical anharmonic spectra provide the water O-H stretches as well as the rotational motion of the water molecule at finite temperature, as observed in the experiment.

Nonrandom γ-TuNA-dependent spatial pattern of microtubule nucleation at the Golgi

PubMed Central

Sanders, Anna A. W. M.; Chang, Kevin; Zhu, Xiaodong; Thoppil, Roslin J.; Holmes, William R.; Kaverina, Irina

2017-01-01

Noncentrosomal microtubule (MT) nucleation at the Golgi generates MT network asymmetry in motile vertebrate cells. Investigating the Golgi-derived MT (GDMT) distribution, we find that MT asymmetry arises from nonrandom nucleation sites at the Golgi (hotspots). Using computational simulations, we propose two plausible mechanistic models of GDMT nucleation leading to this phenotype. In the “cooperativity” model, formation of a single GDMT promotes further nucleation at the same site. In the “heterogeneous Golgi” model, MT nucleation is dramatically up-regulated at discrete and sparse locations within the Golgi. While MT clustering in hotspots is equally well described by both models, simulating MT length distributions within the cooperativity model fits the data better. Investigating the molecular mechanism underlying hotspot formation, we have found that hotspots are significantly smaller than a Golgi subdomain positive for scaffolding protein AKAP450, which is thought to recruit GDMT nucleation factors. We have further probed potential roles of known GDMT-promoting molecules, including γ-TuRC-mediated nucleation activator (γ-TuNA) domain-containing proteins and MT stabilizer CLASPs. While both γ-TuNA inhibition and lack of CLASPs resulted in drastically decreased GDMT nucleation, computational modeling revealed that only γ-TuNA inhibition suppressed hotspot formation. We conclude that hotspots require γ-TuNA activity, which facilitates clustered GDMT nucleation at distinct Golgi sites. PMID:28931596

Sound controlled rotation of a cluster of small particles on an ultrasonically vibrating metal strip

NASA Astrophysics Data System (ADS)

Zhang, Xueyi; Zheng, Yun; Hu, Junhui

2008-01-01

We show that a vibrating metal strip, mechanically driven by an ultrasonic transducer, can rotate a cluster of small particles around a fixed point, and the diameter of the cluster of small particles can reach a stable value (steady diameter) for a given driving condition. The rotation is very stable when the vibration of the metal strip is appropriate. The revolution speed, its direction, and steady diameter of the particle cluster can be controlled by the operating frequency of the ultrasonic transducer. For shrimp eggs, a revolution speed up to 360rpm can be obtained.

Impurity-doped Si10 cluster: Understanding the structural and electronic properties from first-principles calculations

NASA Astrophysics Data System (ADS)

Majumder, Chiranjib; Kulshreshtha, S. K.

2004-12-01

Structural and electronic properties of metal-doped silicon clusters ( MSi10 , M=Li , Be, B, C, Na, Mg, Al, and Si) have been investigated via ab initio molecular dynamics simulation under the formalism of the density functional theory. The exchange-correlation energy has been calculated using the generalized gradient approximation method. Several stable isomers of MSi10 clusters have been identified based on different initial configurations and their relative stabilities have been analyzed. From the results it is revealed that the location of the impurity atom depends on the nature of interaction between the impurity atom and the host cluster and the size of the impurty atom. Whereas Be and B atoms form stable isomers, the impurity atom being placed at the center of the bicapped tetragonal antiprism structure of the Si10 cluster, all other elements diffuse outside the cage of Si10 cluster. Further, to understand the stability and the chemical bonding, the LCAO-MO based all electron calculations have been carried out for the lowest energy isomers using the hybrid B3LYP energy functional. Based on the interaction energy of the M atoms with Si10 clusters it is found that p-p interaction dominates over the s-p interaction and smaller size atoms interact more strongly. Based on the binding energy, the relative stability of MSi10 clusters is found to follow the order of CSi10>BSi10>BeSi10>Si11>AlSi10>LiSi10>NaSi10>MgSi10 , leading one to infer that while the substitution of C, B and Be enhances the stability of the Si11 cluster, others have an opposite effect. The extra stability of the BeSi10 clusters is due to its encapsulated close packed structure and large energy gap between the HOMO and LUMO energy levels.

Triple Halide Bridges in Chiral MnII2MnIII6NaI2 Cages: Structural and Magnetic Characterization.

PubMed

Mayans, Júlia; Font-Bardia, Mercè; Escuer, Albert

2018-02-05

A family of decanuclear chiral clusters with a Mn II 2 Mn III 6 Na I 2 core have been synthesized from enantiomerically pure Schiff bases. The new systems consist of two Mn II Mn III 3 Na I units linked by rare triple chloro or bromo bridges between the divalent Mn cations. Susceptibility measurements point out the weak antiferromagnetic interaction mediated by these kinds of bridges and afford the first magnetic measurements for the (μ-Br) 3 case.

Evolutionary dynamics of avian influenza A H7N9 virus across five waves in mainland China, 2013-2017.

PubMed

Xiang, Dan; Pu, Zhiqing; Luo, Tingting; Guo, Fucheng; Li, Xiaobing; Shen, Xuejuan; Irwin, David M; Murphy, Robert W; Liao, Ming; Shen, Yongyi

2018-05-25

Since its emergence in March 2013, novel avian influenza A H7N9 virus has triggered five epidemics of human infections in China. This raises concerns about the pandemic threat of this quickly evolving H7N9 subtype for humans. In this study, we evaluated all available genomes for H7N9 and H9N2 influenza A viruses. Our assessment discovered that H7N9 of the 1st wave had the lowest nucleotide diversity, which then experienced substantial and rapid population expansion from a small founder population. From the 2nd wave, their nucleotide diversity increased quickly, indicating that H7N9 viruses had acquired larger populations and mutations after their initial emergence in 2013. After the phylogeographic divergence in the 2nd wave, although the HA and NA genes from different regions differed, compared to previous epidemics, the evolving H7N9 viruses in the 5th wave lost most of their previous clades. The highly pathogenic avian influenza (HPAI) H7N9 viruses in the 5th wave clustered together, and clustered close to the low pathogenic avian influenza (LPAI) virus isolated from the Pearl River Delta in the 3rd and 4th waves. This result supports the origin of HPAI H7N9 viruses was in the Pearl River Delta. In the 5th wave, although both HPAI and LPAI H7N9 viruses were isolated from the Pearl River Delta, their HA and NA genes were phylogenetically distinct. Copyright © 2018. Published by Elsevier Ltd.

The Gaia-ESO Survey: Sodium and aluminium abundances in giants and dwarfs. Implications for stellar and Galactic chemical evolution

NASA Astrophysics Data System (ADS)

Smiljanic, R.; Romano, D.; Bragaglia, A.; Donati, P.; Magrini, L.; Friel, E.; Jacobson, H.; Randich, S.; Ventura, P.; Lind, K.; Bergemann, M.; Nordlander, T.; Morel, T.; Pancino, E.; Tautvaišienė, G.; Adibekyan, V.; Tosi, M.; Vallenari, A.; Gilmore, G.; Bensby, T.; François, P.; Koposov, S.; Lanzafame, A. C.; Recio-Blanco, A.; Bayo, A.; Carraro, G.; Casey, A. R.; Costado, M. T.; Franciosini, E.; Heiter, U.; Hill, V.; Hourihane, A.; Jofré, P.; Lardo, C.; de Laverny, P.; Lewis, J.; Monaco, L.; Morbidelli, L.; Sacco, G. G.; Sbordone, L.; Sousa, S. G.; Worley, C. C.; Zaggia, S.

2016-05-01

Context. Stellar evolution models predict that internal mixing should cause some sodium overabundance at the surface of red giants more massive than ~1.5-2.0 M⊙. The surface aluminium abundance should not be affected. Nevertheless, observational results disagree about the presence and/or the degree of Na and Al overabundances. In addition, Galactic chemical evolution models adopting different stellar yields lead to very different predictions for the behavior of [Na/Fe] and [Al/Fe] versus [Fe/H]. Overall, the observed trends of these abundances with metallicity are not well reproduced. Aims: We readdress both issues, using new Na and Al abundances determined within the Gaia-ESO Survey. Our aim is to obtain better observational constraints on the behavior of these elements using two samples: I) more than 600 dwarfs of the solar neighborhood and of open clusters and II) low- and intermediate-mass clump giants in six open clusters. Methods: Abundances were determined using high-resolution UVES spectra. The individual Na abundances were corrected for nonlocal thermodynamic equilibrium effects. For the Al abundances, the order of magnitude of the corrections was estimated for a few representative cases. For giants, the abundance trends with stellar mass are compared to stellar evolution models. For dwarfs, the abundance trends with metallicity and age are compared to detailed chemical evolution models. Results: Abundances of Na in stars with mass below ~2.0 M⊙, and of Al in stars below ~3.0 M⊙, seem to be unaffected by internal mixing processes. For more massive stars, the Na overabundance increases with stellar mass. This trend agrees well with predictions of stellar evolutionary models. For Al, our only cluster with giants more massive than 3.0 M⊙, NGC 6705, is Al enriched. However, this might be related to the environment where the cluster was formed. Chemical evolution models that well fit the observed [Na/Fe] vs. [Fe/H] trend in solar neighborhood dwarfs cannot simultaneously explain the run of [Al/Fe] with [Fe/H], and vice versa. The comparison with stellar ages is hampered by severe uncertainties. Indeed, reliable age estimates are available for only a half of the stars of the sample. We conclude that Al is underproduced by the models, except for stellar ages younger than about 7 Gyr. In addition, some significant source of late Na production seems to be missing in the models. Either current Na and Al yields are affected by large uncertainties, and/or some important Galactic source(s) of these elements has as yet not been taken into account. Based on observations made with the ESO/VLT, at Paranal Observatory, under program 188.B-3002 (The Gaia-ESO Public Spectroscopic Survey), and on data obtained from the ESO Archive originally observed under programs 60.A-9143, 076.B-0263 and 082.D-0726.Table 1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/589/A115

Theoretical research program to study transition metal trimers and embedded clusters

NASA Technical Reports Server (NTRS)

Walch, S. P.

1984-01-01

Small transition metal clusters were studied at a high level of approximation, including all the valence electrons in the calculation and extensive electron correlation, in order to understand the electronic structure of these small metal clusters. By comparison of dimers, trimers, and possibly higher clusters, the information obtained was used to provide insights into the electronic structure of bulk transition metals. Small metal clusters are currently of considerable experimental interest and some information is becomming available both from matrix electron spin resonance studies and from gas phase spectroscopy. Collaboration between theorists and experimentalists is thus expected to be especially profitable at this time since there is some experimental information which can serve to guide the theoretical work.

Preoptimised VB: a fast method for the ground and excited states of ionic clusters I. Localised preoptimisation for (ArCO) +, (ArN 2) + and N 4+

NASA Astrophysics Data System (ADS)

Langenberg, J. H.; Bucur, I. B.; Archirel, P.

1997-09-01

We show that in the simple case of van der Waals ionic clusters, the optimisation of orbitals within VB can be easily simulated with the help of pseudopotentials. The procedure yields the ground and the first excited states of the cluster simultaneously. This makes the calculation of potential energy surfaces for tri- and tetraatomic clusters possible, with very acceptable computation times. We give potential curves for (ArCO) +, (ArN 2) + and N 4+. An application to the simulation of the SCF method is shown for Na +H 2O.

Power and money in cluster randomized trials: when is it worth measuring a covariate?

PubMed

Moerbeek, Mirjam

2006-08-15

The power to detect a treatment effect in cluster randomized trials can be increased by increasing the number of clusters. An alternative is to include covariates into the regression model that relates treatment condition to outcome. In this paper, formulae are derived in order to evaluate both strategies on basis of their costs. It is shown that the strategy that uses covariates is more cost-efficient in detecting a treatment effect when the costs to measure these covariates are small and the correlation between the covariates and outcome is sufficiently large. The minimum required correlation depends on the cluster size, and the costs to recruit a cluster and to measure the covariate, relative to the costs to recruit a person. Measuring a covariate that varies at the person level only is recommended when cluster sizes are small and the costs to recruit and measure a cluster are large. Measuring a cluster level covariate is recommended when cluster sizes are large and the costs to recruit and measure a cluster are small. An illustrative example shows the use of the formulae in a practical setting. Copyright 2006 John Wiley & Sons, Ltd.

WFPC2 Observations of Star Clusters in the Magellanic Clouds. Report 2; The Oldest Star Clusters in the Small Magellanic Cloud

NASA Technical Reports Server (NTRS)

Mighell, Kenneth J.; Sarajedini, Ata; French, Rica S.

1998-01-01

We present our analysis of archival Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2) observations in F45OW ( approximately B) and F555W (approximately V) of the intermediate-age populous star clusters NGC 121, NGC 339, NGC 361, NGC 416, and Kron 3 in the Small Magellanic Cloud. We use published photometry of two other SMC populous star clusters, Lindsay 1 and Lindsay 113, to investigate the age sequence of these seven populous star clusters in order to improve our understanding of the formation chronology of the SMC. We analyzed the V vs B-V and M(sub V) vs (B-V)(sub 0) color-magnitude diagrams of these populous Small Magellanic Cloud star clusters using a variety of techniques and determined their ages, metallicities, and reddenings. These new data enable us to improve the age-metallicity relation of star clusters in the Small Magellanic Cloud. In particular, we find that a closed-box continuous star-formation model does not reproduce the age-metallicity relation adequately. However, a theoretical model punctuated by bursts of star formation is in better agreement with the observational data presented herein.

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

PubMed

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

2011-11-07

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

Alexithymia and emotional regulation: A cluster analytical approach.

PubMed

Chen, Jie; Xu, Ting; Jing, Jin; Chan, Raymond C K

2011-02-23

Alexithymia has been a familiar conception of psychosomatic phenomenon. The aim of this study was to investigate whether there were subtypes of alexithymia associating with different traits of emotional expression and regulation among a group of healthy college students. 1788 healthy college students were administered with the Chinese version of the 20-item Toronto Alexithymia Scale (TAS-20) and another set of questionnaires assessing emotion status and regulation. A hierarchical cluster analysis was conducted on the three factor scores of the TAS-20. The cluster solution was cross-validated by the corresponding emotional regulation. The results indicated there were four subtypes of alexithymia, namely extrovert-high alexithymia (EHA), general-high alexithymia (GHA), introvert-high alexithymia (IHA) and non-alexithymia (NA). The GHA was characterized by general high scores on all three factors, the IHA was characterized by high scores on difficulty identifying feelings and difficulty describing feelings but low score on externally oriented cognitive style of thinking, the EHA was characterized by high score on externally oriented cognitive style of thinking but normal score on the others, and the NA got low score on all factors. The GHA and IHA were dominant by suppressive character of emotional regulation and expression with worse emotion status as compared to the EHA and NA. The current findings suggest there were four subtypes of alexithymia characterized by different emotional regulation manifestations.

Alexithymia and emotional regulation: A cluster analytical approach

PubMed Central

2011-01-01

Background Alexithymia has been a familiar conception of psychosomatic phenomenon. The aim of this study was to investigate whether there were subtypes of alexithymia associating with different traits of emotional expression and regulation among a group of healthy college students. Methods 1788 healthy college students were administered with the Chinese version of the 20-item Toronto Alexithymia Scale (TAS-20) and another set of questionnaires assessing emotion status and regulation. A hierarchical cluster analysis was conducted on the three factor scores of the TAS-20. The cluster solution was cross-validated by the corresponding emotional regulation. Results The results indicated there were four subtypes of alexithymia, namely extrovert-high alexithymia (EHA), general-high alexithymia (GHA), introvert-high alexithymia (IHA) and non-alexithymia (NA). The GHA was characterized by general high scores on all three factors, the IHA was characterized by high scores on difficulty identifying feelings and difficulty describing feelings but low score on externally oriented cognitive style of thinking, the EHA was characterized by high score on externally oriented cognitive style of thinking but normal score on the others, and the NA got low score on all factors. The GHA and IHA were dominant by suppressive character of emotional regulation and expression with worse emotion status as compared to the EHA and NA. Conclusions The current findings suggest there were four subtypes of alexithymia characterized by different emotional regulation manifestations. PMID:21345180

Microglia Morphological Categorization in a Rat Model of Neuroinflammation by Hierarchical Cluster and Principal Components Analysis.

PubMed

Fernández-Arjona, María Del Mar; Grondona, Jesús M; Granados-Durán, Pablo; Fernández-Llebrez, Pedro; López-Ávalos, María D

2017-01-01

It is known that microglia morphology and function are closely related, but only few studies have objectively described different morphological subtypes. To address this issue, morphological parameters of microglial cells were analyzed in a rat model of aseptic neuroinflammation. After the injection of a single dose of the enzyme neuraminidase (NA) within the lateral ventricle (LV) an acute inflammatory process occurs. Sections from NA-injected animals and sham controls were immunolabeled with the microglial marker IBA1, which highlights ramifications and features of the cell shape. Using images obtained by section scanning, individual microglial cells were sampled from various regions (septofimbrial nucleus, hippocampus and hypothalamus) at different times post-injection (2, 4 and 12 h). Each cell yielded a set of 15 morphological parameters by means of image analysis software. Five initial parameters (including fractal measures) were statistically different in cells from NA-injected rats (most of them IL-1β positive, i.e., M1-state) compared to those from control animals (none of them IL-1β positive, i.e., surveillant state). However, additional multimodal parameters were revealed more suitable for hierarchical cluster analysis (HCA). This method pointed out the classification of microglia population in four clusters. Furthermore, a linear discriminant analysis (LDA) suggested three specific parameters to objectively classify any microglia by a decision tree. In addition, a principal components analysis (PCA) revealed two extra valuable variables that allowed to further classifying microglia in a total of eight sub-clusters or types. The spatio-temporal distribution of these different morphotypes in our rat inflammation model allowed to relate specific morphotypes with microglial activation status and brain location. An objective method for microglia classification based on morphological parameters is proposed. Main points Microglia undergo a quantifiable morphological change upon neuraminidase induced inflammation.Hierarchical cluster and principal components analysis allow morphological classification of microglia.Brain location of microglia is a relevant factor.

Microglia Morphological Categorization in a Rat Model of Neuroinflammation by Hierarchical Cluster and Principal Components Analysis

PubMed Central

Fernández-Arjona, María del Mar; Grondona, Jesús M.; Granados-Durán, Pablo; Fernández-Llebrez, Pedro; López-Ávalos, María D.

2017-01-01

It is known that microglia morphology and function are closely related, but only few studies have objectively described different morphological subtypes. To address this issue, morphological parameters of microglial cells were analyzed in a rat model of aseptic neuroinflammation. After the injection of a single dose of the enzyme neuraminidase (NA) within the lateral ventricle (LV) an acute inflammatory process occurs. Sections from NA-injected animals and sham controls were immunolabeled with the microglial marker IBA1, which highlights ramifications and features of the cell shape. Using images obtained by section scanning, individual microglial cells were sampled from various regions (septofimbrial nucleus, hippocampus and hypothalamus) at different times post-injection (2, 4 and 12 h). Each cell yielded a set of 15 morphological parameters by means of image analysis software. Five initial parameters (including fractal measures) were statistically different in cells from NA-injected rats (most of them IL-1β positive, i.e., M1-state) compared to those from control animals (none of them IL-1β positive, i.e., surveillant state). However, additional multimodal parameters were revealed more suitable for hierarchical cluster analysis (HCA). This method pointed out the classification of microglia population in four clusters. Furthermore, a linear discriminant analysis (LDA) suggested three specific parameters to objectively classify any microglia by a decision tree. In addition, a principal components analysis (PCA) revealed two extra valuable variables that allowed to further classifying microglia in a total of eight sub-clusters or types. The spatio-temporal distribution of these different morphotypes in our rat inflammation model allowed to relate specific morphotypes with microglial activation status and brain location. An objective method for microglia classification based on morphological parameters is proposed. Main points Microglia undergo a quantifiable morphological change upon neuraminidase induced inflammation.Hierarchical cluster and principal components analysis allow morphological classification of microglia.Brain location of microglia is a relevant factor. PMID:28848398

Lack of small-scale clustering in 21-cm intensity maps crossed with 2dF galaxy densities at z ~ 0.08

NASA Astrophysics Data System (ADS)

Anderson, Christopher; Luciw, Nicholas; Li, Yi-Chao; Kuo, Cheng-Yu; Yadav, Jaswant; Masui, Kiyoshi; Chang, Tzu-Ching; Chen, Xuelei; Oppermann, Niels; Pen, Ue-Li; Timbie, Peter T.

2017-06-01

I report results from 21-cm intensity maps acquired from the Parkes radio telescope and cross-correlated with galaxy maps from the 2dF galaxy survey. The data span the redshift range 0.057

Encapsulating Metal Clusters and Acid Sites within Small Voids: Synthetic Strategies and Catalytic Consequences

NASA Astrophysics Data System (ADS)

Goel, Sarika

The selective encapsulation of metal clusters within zeolites can be used to prepare clusters that are uniform in diameter and to protect them against sintering and contact with feed impurities, while concurrently allowing active sites to select reactants based on their molecular size, thus conferring enzyme-like specificity to chemical catalysis. The apertures in small and medium-pore zeolites preclude the use of post-synthetic protocols to encapsulate the relevant metal precursors because cationic or anionic precursors with their charge-balancing double layer and gaseous complexes cannot diffuse through their windows or channels. We have developed general strategies to encapsulate metal clusters within small-pore zeolites by using metal precursors stabilized by ammonia or organic amine ligands, which stabilize metal precursors against their premature precipitation at the high temperature and pH conditions required for the hydrothermal synthesis of the target zeolite structures and favor interactions between metal precursors and incipient aluminosilicate nuclei during the self-assembly of microporous frameworks. When synthesis temperatures were higher than 400 K, available ligands were unable to prevent the premature precipitation of the metal precursors. In such cases, encapsulation was achieved instead via interzeolite transformations after successfully encapsulating metal precursors or clusters via post-synthesis exchange or ligand protection into parent zeolites and subsequently converting them into the target structures while retaining the encapsulated clusters or precursors. Such strategies led to the successful selective encapsulation of a wide range of metal clusters (Pt, Pd, Ru, Rh, Ir, Re, and Ag) within small-pore (SOD (sodalite), LTA (Linde type A (zeolite A)), GIS (gismondine), and ANA (analcime)) and medium-pore (MFI (ZSM-5)) zeolites. These protocols provide novel and diverse mechanism-based strategies for the design of catalysts with protected active sites. We have demonstrated the selectivity of the encapsulation processes by combining transmission electron microscopy and chemisorptive titrations with rigorous catalytic assessments of the ability of these materials to catalyze reactions of small molecules, which can access the intracrystalline voids, but not of larger molecules that cannot access the metal clusters within such voids. The selective confinement of clusters also prevented their contact with sulfur compounds (e.g., thiophene and H2S), thus allowing reactions to occur at conditions that otherwise render unconfined clusters unreactive. We have also developed synthetic protocols and guiding principles, inspired by mechanistic considerations, for the synthesis of zeolites via interzeolite transformations without the use of organic structure-directing agents (OSDA). More specifically, we have synthesized high-silica MFI (ZSM-5), CHA (chabazite), STF (SSZ-35) and MTW (ZSM-12) zeolites from FAU (faujasite) or BEA (beta) parent materials. Structures with lower framework densities (FAU or BEA) were successfully transformed into thermodynamically-favored, more stable structures with higher framework densities (MFI, CHA, STF, and MTW); to date, target materials with higher Si/Al ratios (Si/Al >10) have not been synthesized via interzeolite transformations without the aid of the OSDA species used to discover these zeolite structures and deemed essential up until now for their successful synthesis. Overcoming kinetic hurdles in such transformations required either the presence of common composite building units (CBU) between parent and target structures or, in their absence, the introduction of small amount of seeds of the daughter structures. The NaOH/SiO2 ratio, H2O/SiO2 ratio and Al content in reagents are used to enforce synchronization between the swelling and local restructuring within parent zeolite domains with the spalling of fragments or building units from seeds of the target structure. The pseudomorphic nature of these seed-mediated transformations, which conserve the volume occupied by the parent crystals and lead to similar size and crystal shape in products, reflect incipient nucleation of target structures occurring at the outer regions of the parent domains and lead to the formation of mesoporosity as a natural consequence of the space-conserving nature of these structural changes and of the higher density of the daughter frameworks. The synthesis mechanism and the guidelines developed enable us to enforce conditions required for the formation of zeolites that previously required OSDA species for their synthesis, thus expanding to a significant extent the diversity of zeolite frameworks that are accessible via these synthesis protocols and providing potential savings in the time and cost involved in the synthesis of some of these zeolite structures.

Method and apparatus for detecting and/or imaging clusters of small scattering centers in the body

DOEpatents

Perez-Mendez, V.; Sommer, F.G.

1982-07-13

An ultrasonic method and apparatus are provided for detecting and imaging clusters of small scattering centers in the breast wherein periodic pulses are applied to an ultrasound emitting transducer and projected into the body, thereafter being received by at least one receiving transducer positioned to receive scattering from the scattering center clusters. The signals are processed to provide an image showing cluster extent and location. 6 figs.

Method and apparatus for detecting and/or imaging clusters of small scattering centers in the body

DOEpatents

Perez-Mendez, Victor; Sommer, Frank G.

1982-01-01

An ultrasonic method and apparatus are provided for detecting and imaging clusters of small scattering centers in the breast wherein periodic pulses are applied to an ultrasound emitting transducer and projected into the body, thereafter being received by at least one receiving transducer positioned to receive scattering from the scattering center clusters. The signals are processed to provide an image showing cluster extent and location.

Hot and solid gallium clusters: too small to melt.

PubMed

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

2003-11-21

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

Sodium alginate inhibits methotrexate-induced gastrointestinal mucositis in rats.

PubMed

Yamamoto, Atsuki; Itoh, Tomokazu; Nasu, Reishi; Kajiwara, Eiji; Nishida, Ryuichi

2013-01-01

Gastrointestinal mucositis is one of the most prevalent side effects of chemotherapy. Methotrexate is a pro-oxidant compound that depletes dihydrofolate pools and is widely used in the treatment of leukemia and other malignancies. Through its effects on normal tissues with high rates of proliferation, methotrexate treatment leads to gastrointestinal mucositis. In rats, methotrexate-induced gastrointestinal mucositis is histologically characterized by crypt loss, callus fusion and atrophy, capillary dilatation, and infiltration of mixed inflammatory cells. The water-soluble dietary fiber sodium alginate (AL-Na) is derived from seaweed and has demonstrated muco-protective and hemostatic effects on upper gastrointestinal ulcers. In the present study, we evaluated the effects of AL-Na on methotrexate-induced small intestinal mucositis in rats. Animals were subcutaneously administered methotrexate at a dosage of 2.5 mg/kg once daily for 3 d. Rats were treated with single oral doses of AL-Na 30 min before and 6 h after methotrexate administration. On the 4th day, small intestines were removed and weighed. Subsequently, tissues were stained with hematoxylin-eosin and bromodeoxyuridine. AL-Na significantly prevented methotrexate-induced small intestinal mucositis. Moreover, AL-Na prevented decreases in red blood cell numbers, hemoglobin levels, and hematocrit levels. These results suggest the potential of AL-Na as a therapy for methotrexate-induced small intestinal mucositis.

p-capture reaction cycles in rotating massive stars and their impact on elemental abundances in globular cluster stars: A case study of O, Na and Al

NASA Astrophysics Data System (ADS)

Mahanta, Upakul; Goswami, Aruna; Duorah, Hiralal; Duorah, Kalpana

2017-08-01

Elemental abundance patterns of globular cluster stars can provide important clues for understanding cluster formation and early chemical evolution. The origin of the abundance patterns, however, still remains poorly understood. We have studied the impact of p-capture reaction cycles on the abundances of oxygen, sodium and aluminium considering nuclear reaction cycles of carbon-nitrogen-oxygen-fluorine, neon-sodium and magnesium-aluminium in massive stars in stellar conditions of temperature range 2×107 to 10×107 K and typical density of 102 gm cc-1. We have estimated abundances of oxygen, sodium and aluminium with respect to Fe, which are then assumed to be ejected from those stars because of rotation reaching a critical limit. These ejected abundances of elements are then compared with their counterparts that have been observed in some metal-poor evolved stars, mainly giants and red giants, of globular clusters M3, M4, M13 and NGC 6752. We observe an excellent agreement with [O/Fe] between the estimated and observed abundance values for globular clusters M3 and M4 with a correlation coefficient above 0.9 and a strong linear correlation for the remaining two clusters with a correlation coefficient above 0.7. The estimated [Na/Fe] is found to have a correlation coefficient above 0.7, thus implying a strong correlation for all four globular clusters. As far as [Al/Fe] is concerned, it also shows a strong correlation between the estimated abundance and the observed abundance for globular clusters M13 and NGC 6752, since here also the correlation coefficient is above 0.7 whereas for globular cluster M4 there is a moderate correlation found with a correlation coefficient above 0.6. Possible sources of these discrepancies are discussed.

A combined gene and cell therapy approach for restoration of conduction.

PubMed

Hofshi, Anat; Itzhaki, Ilanit; Gepstein, Amira; Arbel, Gil; Gross, Gil J; Gepstein, Lior

2011-01-01

Abnormal conduction underlies both bradyarrhythmias and re-entrant tachyarrhythmias. However, no practical way exists for restoring or improving conduction in areas of conduction slowing or block. This study sought to test the feasibility of a novel strategy for conduction repair using genetically engineered cells designed to form biological "conducting cables." An in vitro model of conduction block was established using spatially separated, spontaneously contracting, nonsynchronized human embryonic stem cell-derived cardiomyocytes clusters. Immunostaining, dye transfer, intracellular recordings, and multielectrode array (MEA) studies were performed to evaluate the ability of genetically engineered HEK293 cells, expressing the SCN5A-encoded Na(+) channel, to couple with cultured cardiomyocytes and to synchronize their electrical activity. Connexin-43 immunostaining and calcein dye-transfer experiments confirmed the formation of functional gap junctions between the engineered cells and neighboring cardiomyocytes. MEA and intracellular recordings were performed to assess the ability of the engineered cells to restore conduction in the co-cultures. Synchronization was defined by establishment of fixed local activation time differences between the cardiomyocytes clusters and convergence of their activation cycle lengths. Nontransfected control cells were able to induce synchronization between cardiomyocytes clusters separated by distances up to 300 μm (n = 21). In contrast, the Na(+) channel-expressing cells synchronized contractions between clusters separated by up to 1,050 μm, the longest distance studied (n = 23). Finally, engineered cells expressing the voltage-sensitive K(v)1.3 potassium channel prevented synchronization at any distance. Genetically engineered cells, transfected to express Na(+) channels, can form biological conducting cables bridging and coupling spatially separated cardiomyocytes. This novel cell therapy approach might be useful for the development of therapeutic strategies for both bradyarrhythmias and tachyarrhythmias. Copyright © 2011 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.

Real-time analysis of self-assembled nucleobases by Venturi easy ambient sonic-spray ionization mass spectrometry.

PubMed

Na, Na; Shi, Ruixia; Long, Zi; Lu, Xin; Jiang, Fubin; Ouyang, Jin

2014-10-01

In this study, the real-time analysis of self-assembled nucleobases was employed by Venturi easy ambient sonic-spray ionization mass spectrometry (V-EASI-MS). With the analysis of three nucleobases including 6-methyluracil (6MU), uracil (U) and thymine (T) as examples, different orders of clusters centered with different metal ions were recorded in both positive and negative modes. Compared with the results obtained by traditional electrospray ionization mass spectrometry (ESI-MS) under the same condition, more clusters with high orders, such as [6MU7+Na](+), [6MU15+2NH4](2+), [6MU10+Na](+), [T7+Na](+), and [T15+2NH4](2+) were detected by V-EASI-MS, which demonstrated the soft ionization ability of V-EASI for studying the non-covalent interaction in a self-assembly process. Furthermore, with the injection of K(+) to the system by a syringe pumping, the real-time monitoring of the formation of nucleobases clusters was achieved by the direct extraction of samples from the system under the Venturi effect. Therefore, the effect of cations on the formation of clusters during self-assembly of nucleobases was demonstrated, which was in accordance with the reports. Free of high voltage, heating or radiation during the ionization, this technique is much soft and suitable for obtaining the real-time information of the self-assembly system, which also makes it quite convenient for extraction samples from the reaction system. This "easy and soft" ionization technique has provided a potential pathway for monitoring and controlling the self-assembly processes. Copyright © 2014 Elsevier B.V. All rights reserved.

Cohesive Energies of Some Transition Metal Compounds Using Embedded Clusters

NASA Astrophysics Data System (ADS)

Press, Mehernosh Rustom

The molecular-clusters approach to electronic structure calculation is especially well-suited to the study of properties that depend primarily on the local environment of a system, especially those with no translational symmetry, e.g. systems with defects and structural deformations. The presence of the rest of the crystal environment can be accounted for approximately by embedding the cluster in a self-consistent crystal potential. This thesis makes a contribution in the area of investigating the capability of embedded molecular-clusters to yield reliable bulk structural properties. To this end, an algorithm for calculating the cohesive energies of clusters within the discrete-variational X(,(alpha)) LCAO-MO formulation is set up and verified on simple solids: Li, Na, Cu and LiF. We then use this formulation to study transition metal compounds, for which the interesting physics lies in local lattice defects, foreign impurities and structural deformations. In a self -consistent calculation of the lattice energies and stability of defect clusters in wustite, Fe(,1-x)O, corner-sharing aggregates of the 4:1 defect are identified as the most stable defect configurations due to efficient compensation of the cluster charge. The intercalation properties of layered-transition-metal-dichalcogenides continues to be a fertile experimental working area, backed by comparatively little theoretical study. We find that intercalation of ZrS(,2) with Na perturbs the valence energy level structure sufficiently to induce a more ionic Zr-S bond, a narrowing of the optical gap and filling of the lowest unoccupied host lattice orbitals with the electron donated by Na. Fe - intercalation in ZrS(,2) is accommodated via a strong Fe-S bond, impurity-like band levels in the optical gap of the host and hybridization-driven compression and lowering of the conduction band energy levels. The piezoelectric cuprous halides, CuCl and CuBr, exhibit a host of intriguing properties due to a filled and very active d('10) shell at the Fermi energy. A self-consistent calculation via energy minimization of the internal strain in these compounds shows both Cu-halide bonds to be very rigid with little charge delocalization under strain. Piezoelectric response is calculated in terms of effective charges and quadrupolar moments, e(,T) and (DELTA)Q.

Abundance differences among globular-cluster giants: Primordial versus evolutionary scenarios

NASA Astrophysics Data System (ADS)

Kraft, Robert P.

1994-06-01

Contrary to historical expectation, stars within a given globular cluster often exhibit wide variations in the abundance of C, N, and O as well as certain light metals, particularly Na and Al. Owing to flux limitations, studies have been confined to evolved stars, especially giants, but in few instances variations have been detected among main-sequence stars. Among giants, the variations are of two kinds. The abundances of C and N are often anticorrelated, and in the limited number of cases in which both have been measured, O and N abundances have also often proved to be anticorrelated (Pilachowski 1988; Sneden et al. 1991; Brown et al. 1991; Kraft et al. 1992). Following pioneering work by Cohen (1978) and Peterson (1980), strong evidence has recently emerged for the existence of a significant global anticorrelation between O and Na abundances (Drake et al. 1992, Kraft et al. 1993). The observations are discussed in terms of contrasting hypotheses: evolutionary versus primordial. In the former, the variations are attributed to the dredgeup of material that has been processed through the CNO cycle in the globular-cluster stars themselves. In the latter, the variations are attributed to primordial chemical inhomogeneities in the material out of which the cluster stars were formed, the composition of these 'clumps' having been determined by nuclear processing in a prior generation of more massive stars. Observational evidence supporting each of these scenarios is cited. Recent studies of stellar rotation among horizontal branch stars in certain clusters (Peterson et al. 1994) as well as new calculations of Na-23 and Al-27 production in the CNO processing regions of evolving low-mass giants (Langer et al. 1993) lend fresh support to the evolutionary hypothesis. However, such calculations do not explain the variation of C and N abundances found among cluster main-sequence stars (Suntzeff 1989; Briley et al. 1991) which therefore seem explicable only on the basis of a primordial scenario. Among mildly metal-poor giants, i.e., those in the range from solar metallicity to (Fe/H) approximately -1, recent observational evidence suggesting the existence of a substructure in the (el/Fe) ratios of the heavier alpha elements, e.g., Si, Mg, Ca, and Ti, is discussed. The possible influence of this effect on the interpretation of the integrated spectra of extragalactic globular clusters and E galaxies is noted.

Ab initio structures and polarizabilities of sodium clusters

NASA Astrophysics Data System (ADS)

Kronik, Leeor; Vasiliev, Igor; Jain, Manish; Chelikowsky, James R.

2001-09-01

We present quantitative ab initio calculations for Na cluster structures and polarizabilities, for all cluster sizes up to 20 atoms. Our calculations are performed by combining an ab initio core-corrected pseudopotential and a gradient-corrected density functional within a real space approach. We find the cluster bonding to be very floppy and catalog a host of low-energy quasi-degenerate isomers for all second-decade clusters. The existence of these isomers results in a band of polarizability values for each cluster size even at zero temperature. This eliminates any finer structure in the polarizability curve. We further show that the experimental polarizability values are consistently underestimated by calculations at zero temperature. By computing the effects of structure expansion and distortion due to a finite temperature we arrive at a quantitative agreement between theory and experiment.

Crystallization of the Na+-translocating NADH:quinone oxidoreductase from Vibrio cholerae

PubMed Central

Casutt, Marco S.; Wendelspiess, Severin; Steuber, Julia; Fritz, Günter

2010-01-01

The Na+-translocating NADH:quinone oxidoreductase (Na+-NQR) from the human pathogen Vibrio cholerae couples the exergonic oxidation of NADH by membrane-bound quinone to Na+ translocation across the membrane. Na+-NQR consists of six different subunits (NqrA–NqrF) and contains a [2Fe–2S] cluster, a noncovalently bound FAD, a noncovalently bound riboflavin, two covalently bound FMNs and potentially Q8 as cofactors. Initial crystallization of the entire Na+-NQR complex was achieved by the sitting-drop method using a nanolitre dispenser. Optimization of the crystallization conditions yielded flat yellow-coloured crystals with dimensions of up to 200 × 80 × 20 µm. The crystals diffracted to 4.0 Å resolution and belonged to space group P21, with unit-cell parameters a = 94, b = 146, c = 105 Å, α = γ = 90, β = 111°. PMID:21139223

Eclogite-facies guyanaite, carmichaelite and eskolaite in xenoliths of Cr-omphacitite from Navajo diatremes, Utah: Hydration and dehydration in the subducted Farallon plate

NASA Astrophysics Data System (ADS)

Schulze, D. J.; Helmstaedt, H.

2013-12-01

The mantle-derived xenolith suite in the Navajo serpentinized ultramafic diatremes includes low-temperature metamorphic rocks such as lawsonite- and phengite-bearing eclogites, Cr-pyrope xenocrysts with inclusions of hydrous minerals and hydrated peridotites and pyroxenites containing minerals such as chlorite, pargasite, tremolite and antigorite. We have now also identified a suite of bright green Cr-rich clinopyroxenites from the Moses Rock and Mule's Ear diatremes that contain unusual assemblages of dark to opaque accessory minerals such as guyanaite [CrOOH], carmichaelite [(Ti,Cr)2-x(OH)x], eskolaite [Cr2O3], chromite and rutile. The xenoliths are dominated by omphacitic pyroxenes (most in the range 10-55 mole% jadeite) that are locally enriched in Cr adjacent to clots of accessory minerals (to 35 mole% kosmochlor). Most samples have small clusters of scattered accessory minerals (individual grains on the scale of tens of microns) but one sample has clusters to 2 mm dominated by guyanaite blades intergrown with Cr-rich omphacite. Thin grains of eskolaite traverse the guyanaite and occur at the guyanaite-omphacite interfaces. Patches of zincian chromite (to 5.7 wt% ZnO) are associated with some of the guyanaite-dominated clusters and consist of lamellar intergrowths of two texturally and compositionally different types of chromite, interpreted as an exsolution feature and precursor to hydration and metasomatic development of guyanaite-omphacite intergrowths. Minor carmichaelite occurs in these clusters. In another sample carmichaelite with finely intergrown patches of rutile dominates the clusters. Equilibration conditions of these assemblages are poorly constrained, but the reaction guyanaite = eskolaite + H2O (Jahn et al., Eur. J. Min., 2012) is consistent with an estimate for equilibration conditions of a phengite eclogite (700oC, 3.4GPa - Smith et al., GGG, 2013). We interpret these rocks to be Na-metasomatized and hydrated basalts (small clusters) and peridotites (clusters to 2mm), formed in serpentinites during subduction of the Farallon Plate under the Colorado Plateau in Laramide time, based on similarities with subduction-origin Cr-jade bodies associated with serpentinites (e.g., Myanmar). At the time of entrainment in the host diatremes, these rocks were undergoing dehydration reactions (guyanaite to eskolaite, carmichaelite to rutile) providing water to the overlying subcrustal mantle section and contributing to Plateau uplift. The occurrence of carmichaelite as inclusions armoured within pyrope garnet xenocrysts from the nearby Garnet Ridge diatreme is now linked to the presence of carmichaelite in the open system of the upper mantle in these Cr-omphacitites (the only two known occurrences of carmichaelite), complicating interpretation of the pyropes as being derived from subcontinental upper mantle formed by Proterozoic subduction.

Magic Numbers in Small Iron Clusters: A First-Principles Study

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

Kim, Eunja; Mohrland, Andrew B.; Weck, Philippe F.

2014-10-03

We perform ab initio spin-polarized density functional calculations of Fen aggregates with n ≤ 17 atoms to reveal the origin of the observed magic numbers, which indicate particularly high stability of clusters with 7, 13 and 15 atoms. Our results clarify the controversy regarding the ground state geometry of clusters such as Fe5and indicate that magnetism plays an important role in determining the stability and magic numbers in small iron clusters.

Ruprecht 106: The first single population globular cluster?

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

Villanova, S.; Geisler, D.; Muñoz, C.

2013-12-01

All old Galactic globular clusters (GCs) studied in detail to date host at least two generations of stars, where the second is formed from gas polluted by processed material produced by massive stars of the first. This process can happen if the initial mass of the cluster exceeds a threshold above which ejecta are retained and a second generation is formed. A determination of this mass threshold is mandatory in order to understand how GCs form. We analyzed nine red giant branch stars belonging to the cluster Ruprecht 106. Targets were observed with the UVES@VLT2 spectrograph. Spectra cover a widemore » range and allowed us to measure abundances for light (O, Na, Mg, Al), α (Si, Ca, Ti), iron-peak (Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn), and neutron-capture (Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu, Dy, Pb) elements. Based on these abundances, we show that Ruprecht 106 is the first convincing example of a single-population GC (i.e., a true simple stellar population), although the sample is relatively small. This result is supported also by an independent photometric test and by the horizontal branch morphology and the dynamical state. It is old (∼12 Gyr) and, at odds with other GCs, has no α-enhancement. The material it formed from was contaminated by both s- and r-process elements. The abundance pattern points toward an extragalactic origin. Its present-day mass (M = 10{sup 4.83} M {sub ☉}) can be assumed as a strong lower limit for the initial mass threshold below which no second generation is formed. Clearly, its initial mass must have been significantly greater, but we have no current constraints on the amount of mass loss during its evolution.« less

Two-Photon Na+ Imaging Reports Somatically Evoked Action Potentials in Rat Olfactory Bulb Mitral and Granule Cell Neurites.

PubMed

Ona-Jodar, Tiffany; Gerkau, Niklas J; Sara Aghvami, S; Rose, Christine R; Egger, Veronica

2017-01-01

Dendrodendritic synaptic interactions are a hallmark of neuronal processing in the vertebrate olfactory bulb. Many classes of olfactory bulb neurons including the principal mitral cells (MCs) and the axonless granule cells (GCs) dispose of highly efficient propagation of action potentials (AP) within their dendrites, from where they can release transmitter onto each other. So far, backpropagation in GC dendrites has been investigated indirectly via Ca 2+ imaging. Here, we used two-photon Na + imaging to directly report opening of voltage-gated sodium channels due to AP propagation in both cell types. To this end, neurons in acute slices from juvenile rat bulbs were filled with 1 mM SBFI via whole-cell patch-clamp. Calibration of SBFI signals revealed that a change in fluorescence Δ F / F by 10% corresponded to a Δ[Na + ] i of ∼22 mM. We then imaged proximal axon segments of MCs during somatically evoked APs (sAP). While single sAPs were detectable in ∼50% of axons, trains of 20 sAPs at 50 Hz always resulted in substantial Δ F / F of ∼15% (∼33 mM Δ[Na + ] i ). Δ F / F was significantly larger for 80 Hz vs. 50 Hz trains, and decayed with half-durations τ 1/2 ∼0.6 s for both frequencies. In MC lateral dendrites, AP trains yielded small Δ F / F of ∼3% (∼7 mM Δ[Na + ] i ). In GC apical dendrites and adjacent spines, single sAPs were not detectable. Trains resulted in an average dendritic Δ F / F of 7% (16 mM Δ[Na + ] i ) with τ 1/2 ∼1 s, similar for 50 and 80 Hz. Na + transients were indistinguishable between large GC spines and their adjacent dendrites. Cell-wise analysis revealed two classes of GCs with the first showing a decrease in Δ F / F along the dendrite with distance from the soma and the second an increase. These classes clustered with morphological parameters. Simulations of Δ[Na + ] i replicated these behaviors via negative and positive gradients in Na + current density, assuming faithful AP backpropagation. Such specializations of dendritic excitability might confer specific temporal processing capabilities to bulbar principal cell-GC subnetworks. In conclusion, we show that Na + imaging provides a valuable tool for characterizing AP invasion of MC axons and GC dendrites and spines.

Two-Photon Na+ Imaging Reports Somatically Evoked Action Potentials in Rat Olfactory Bulb Mitral and Granule Cell Neurites

PubMed Central

Ona-Jodar, Tiffany; Gerkau, Niklas J.; Sara Aghvami, S.; Rose, Christine R.; Egger, Veronica

2017-01-01

Dendrodendritic synaptic interactions are a hallmark of neuronal processing in the vertebrate olfactory bulb. Many classes of olfactory bulb neurons including the principal mitral cells (MCs) and the axonless granule cells (GCs) dispose of highly efficient propagation of action potentials (AP) within their dendrites, from where they can release transmitter onto each other. So far, backpropagation in GC dendrites has been investigated indirectly via Ca2+ imaging. Here, we used two-photon Na+ imaging to directly report opening of voltage-gated sodium channels due to AP propagation in both cell types. To this end, neurons in acute slices from juvenile rat bulbs were filled with 1 mM SBFI via whole-cell patch-clamp. Calibration of SBFI signals revealed that a change in fluorescence ΔF/F by 10% corresponded to a Δ[Na+]i of ∼22 mM. We then imaged proximal axon segments of MCs during somatically evoked APs (sAP). While single sAPs were detectable in ∼50% of axons, trains of 20 sAPs at 50 Hz always resulted in substantial ΔF/F of ∼15% (∼33 mM Δ[Na+]i). ΔF/F was significantly larger for 80 Hz vs. 50 Hz trains, and decayed with half-durations τ1/2 ∼0.6 s for both frequencies. In MC lateral dendrites, AP trains yielded small ΔF/F of ∼3% (∼7 mM Δ[Na+]i). In GC apical dendrites and adjacent spines, single sAPs were not detectable. Trains resulted in an average dendritic ΔF/F of 7% (16 mM Δ[Na+]i) with τ1/2 ∼1 s, similar for 50 and 80 Hz. Na+ transients were indistinguishable between large GC spines and their adjacent dendrites. Cell-wise analysis revealed two classes of GCs with the first showing a decrease in ΔF/F along the dendrite with distance from the soma and the second an increase. These classes clustered with morphological parameters. Simulations of Δ[Na+]i replicated these behaviors via negative and positive gradients in Na+ current density, assuming faithful AP backpropagation. Such specializations of dendritic excitability might confer specific temporal processing capabilities to bulbar principal cell-GC subnetworks. In conclusion, we show that Na+ imaging provides a valuable tool for characterizing AP invasion of MC axons and GC dendrites and spines. PMID:28293175

Surface enhanced Raman spectroscopy (SERS) from a molecule adsorbed on a nanoscale silver particle cluster in a holographic plate

NASA Astrophysics Data System (ADS)

Jusinski, Leonard E.; Bahuguna, Ramen; Das, Amrita; Arya, Karamjeet

2006-02-01

Surface enhanced Raman spectroscopy has become a viable technique for the detection of single molecules. This highly sensitive technique is due to the very large (up to 14 orders in magnitude) enhancement in the Raman cross section when the molecule is adsorbed on a metal nanoparticle cluster. We report here SERS (Surface Enhanced Raman Spectroscopy) experiments performed by adsorbing analyte molecules on nanoscale silver particle clusters within the gelatin layer of commercially available holographic plates which have been developed and fixed. The Ag particles range in size between 5 - 30 nanometers (nm). Sample preparation was performed by immersing the prepared holographic plate in an analyte solution for a few minutes. We report here the production of SERS signals from Rhodamine 6G (R6G) molecules of nanomolar concentration. These measurements demonstrate a fast, low cost, reproducible technique of producing SERS substrates in a matter of minutes compared to the conventional procedure of preparing Ag clusters from colloidal solutions. SERS active colloidal solutions require up to a full day to prepare. In addition, the preparations of colloidal aggregates are not consistent in shape, contain additional interfering chemicals, and do not generate consistent SERS enhancement. Colloidal solutions require the addition of KCl or NaCl to increase the ionic strength to allow aggregation and cluster formation. We find no need to add KCl or NaCl to create SERS active clusters in the holographic gelatin matrix. These holographic plates, prepared using simple, conventional procedures, can be stored in an inert environment and preserve SERS activity after several weeks subsequent to preparation.

Chemical Abundances of Seven Outer Halo M31 Globular Clusters from the Pan-Andromeda Archaeological Survey

NASA Astrophysics Data System (ADS)

Sakari, Charli M.

2017-03-01

Observations of stellar streams in M31's outer halo suggest that M31 is actively accreting several dwarf galaxies and their globular clusters (GCs). Detailed abundances can chemically link clusters to their birth environments, establishing whether or not a GC has been accreted from a satellite dwarf galaxy. This talk presents the detailed chemical abundances of seven M31 outer halo GCs (with projected distances from M31 greater than 30 kpc), as derived from high-resolution integrated-light spectra taken with the Hobby Eberly Telescope. Five of these clusters were recently discovered in the Pan-Andromeda Archaeological Survey (PAndAS)-this talk presents the first determinations of integrated Fe, Na, Mg, Ca, Ti, Ni, Ba, and Eu abundances for these clusters. Four of the target clusters (PA06, PA53, PA54, and PA56) are metal-poor ([Fe/H] < -1.5), α-enhanced (though they are possibly less alpha-enhanced than Milky Way stars at the 1 sigma level), and show signs of star-to-star Na and Mg variations. The other three GCs (H10, H23, and PA17) are more metal-rich, with metallicities ranging from [Fe/H] = -1.4 to -0.9. While H23 is chemically similar to Milky Way field stars, Milky Way GCs, and other M31 clusters, H10 and PA17 have moderately-low [Ca/Fe], compared to Milky Way field stars and clusters. Additionally, PA17's high [Mg/Ca] and [Ba/Eu] ratios are distinct from Milky Way stars, and are in better agreement with the stars and clusters in the Large Magellanic Cloud (LMC). None of the clusters studied here can be conclusively linked to any of the identified streams from PAndAS; however, based on their locations, kinematics, metallicities, and detailed abundances, the most metal-rich PAndAS clusters H23 and PA17 may be associated with the progenitor of the Giant Stellar Stream, H10 may be associated with the SW Cloud, and PA53 and PA56 may be associated with the Eastern Cloud.

On the Clustering of Europa's Small Craters

NASA Technical Reports Server (NTRS)

Bierhaus, E. B.; Chapman, C. R.; Merline, W. J.

2001-01-01

We analyze the spatial distribution of Europa's small craters and find that many are too tightly clustered to result from random, primary impacts. Additional information is contained in the original extended abstract.

Type A-B carbonate chlorapatite synthesized at high pressure

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

Fleet, Michael E.; Liu, Xi

2008-09-15

Sodium-bearing type A-B carbonate chlorapatites {l_brace}CCLAP; Ca{sub 10-(y+z)}Na{sub y}{open_square}{sub z}[(PO{sub 4}){sub 6-(y+2z)}(CO{sub 3}){sub y+2z}][Cl{sub 2-=} 2{sub x}(CO{sub 3}){sub x}], with x{approx}y{approx}4z{approx}0.4{r_brace} have been synthesized from carbonate-rich melts at 1350-1000 deg. C and 1.0 GPa, and investigated by single-crystal X-ray structure and FTIR spectroscopy. Typical crystal and compositional data are: a=9.5321(4) A, c=6.8448(3) A, space group P6{sub 3}/m, R=0.027, R{sub w}=0.025, x=0.37(3), y=0.57(2). Crystal-chemical features and FTIR spectra are similar to Na-bearing type A-B carbonate hydroxyapatites (CHAP) and fluorapatites (CFAP) reported recently. The molar amounts of Na and channel (type A) carbonate maintain a near 1:1 ratio in all three compositionmore » series, confirming that the Na cation and A and B carbonate ion substituents exist as a defect cluster within the apatite matrix, to facilitate charge compensation and spatial accommodation. Uptake of carbonate is significantly lower in CCLAP than in CHAP for similar conditions of crystal synthesis. - Graphical abstract: Defect cluster (blue) of A carbonate ion in apatite channel, Na{sup +} cation, and B carbonate ion replacing phosphate group, in carbonate chlorapatite synthesized at high pressure.« less

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

Ben-Naim, Eli; Krapivsky, Paul

Here we generalize the ordinary aggregation process to allow for choice. In ordinary aggregation, two random clusters merge and form a larger aggregate. In our implementation of choice, a target cluster and two candidate clusters are randomly selected and the target cluster merges with the larger of the two candidate clusters.We study the long-time asymptotic behavior and find that as in ordinary aggregation, the size density adheres to the standard scaling form. However, aggregation with choice exhibits a number of different features. First, the density of the smallest clusters exhibits anomalous scaling. Second, both the small-size and the large-size tailsmore » of the density are overpopulated, at the expense of the density of moderate-size clusters. Finally, we also study the complementary case where the smaller candidate cluster participates in the aggregation process and find an abundance of moderate clusters at the expense of small and large clusters. Additionally, we investigate aggregation processes with choice among multiple candidate clusters and a symmetric implementation where the choice is between two pairs of clusters.« less

Silver Creek: A Study of Stream Velocities and Erosion along the Ohio River near Clarksville, Indiana; McAlpine Lock and Dam Numerical Model

DTIC Science & Technology

2018-04-12

split between the upper and lower gates, the tainter gate outflow can cause flow circulations or eddies to form , which requires the use of a multi...determined to not erode were assigned a bed layer thickness of zero. This included the stone weir, fossil beds, non-erodible vegetation, and upstream...606.7 Chute 0.1 606 L 0.4 Erodible Small Vegetation 606.7 Chute 0.1 606 L 0.4 Fossil Bed NA 0 NA 0 Non Erodible Small Vegetation NA 0 NA 0 Non

78 FR 42042 - Taking of Marine Mammals Incidental to Specified Activities; U.S. Marine Corps Training Exercises...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-07-15

.... The types of ordnances proposed for use at BT-9 and BT- 11 include small arms, large arms, bombs...) 48 48 4.8 Rockets--5.0'' (live) 20 20 15.0 Rockets--2.75'' and 5'' (inert) 876 NA N/A Bombs and G911 grenades (live) 0 NA 0.5 Bombs and grenades (inert) 4,199 NA NA Missile--TOW 0 NA NA Missile--Hellfire 0 NA...

Vacancy defects and defect clusters in alkali metal ion-doped MgO nanocrystallites studied by positron annihilation and photoluminescence spectroscopy

NASA Astrophysics Data System (ADS)

Sellaiyan, S.; Uedono, A.; Sivaji, K.; Janet Priscilla, S.; Sivasankari, J.; Selvalakshmi, T.

2016-10-01

Pure and alkali metal ion (Li, Na, and K)-doped MgO nanocrystallites synthesized by solution combustion technique have been studied by positron lifetime and Doppler broadening spectroscopy methods. Positron lifetime analysis exhibits four characteristic lifetime components for all the samples. Doping reduces the Mg vacancy after annealing to 800 °C. It was observed that Li ion migrates to the vacancy site to recover Mg vacancy-type defects, reducing cluster vacancies and micropores. For Na- and K-doped MgO, the aforementioned defects are reduced and immobile at 800 °C. Coincidence Doppler broadening studies show the positron trapping sites as vacancy clusters. The decrease in the S parameter is due to the particle growth and reduction in the defect concentration at 800 °C. Photoluminescence study shows an emission peak at 445 nm and 498 nm, associated with F2 2+ and recombination of higher-order vacancy complexes. Further, annealing process is likely to dissociate F2 2+ to F+ and this F+ is converted into F centers at 416 nm.

Computational Design of Clusters for Catalysis

NASA Astrophysics Data System (ADS)

Jimenez-Izal, Elisa; Alexandrova, Anastassia N.

2018-04-01

When small clusters are studied in chemical physics or physical chemistry, one perhaps thinks of the fundamental aspects of cluster electronic structure, or precision spectroscopy in ultracold molecular beams. However, small clusters are also of interest in catalysis, where the cold ground state or an isolated cluster may not even be the right starting point. Instead, the big question is: What happens to cluster-based catalysts under real conditions of catalysis, such as high temperature and coverage with reagents? Myriads of metastable cluster states become accessible, the entire system is dynamic, and catalysis may be driven by rare sites present only under those conditions. Activity, selectivity, and stability are highly dependent on size, composition, shape, support, and environment. To probe and master cluster catalysis, sophisticated tools are being developed for precision synthesis, operando measurements, and multiscale modeling. This review intends to tell the messy story of clusters in catalysis.

OGLE Collection of Star Clusters. New Objects in the Magellanic Bridge and the Outskirts of the Small Magellanic Cloud

NASA Astrophysics Data System (ADS)

Sitek, M.; Szymański, M. K.; Udalski, A.; Skowron, D. M.; Kostrzewa-Rutkowska, Z.; Skowron, J.; Karczmarek, P.; Cieślar, M.; Wyrzykowski, Ł.; Kozłowski, S.; Pietrukowicz, P.; Soszyński, I.; Mróz, P.; Pawlak, M.; Poleski, R.; Ulaczyk, K.

2017-12-01

The Magellanic System (MS) encompasses the nearest neighbors of the Milky Way, the Large (LMC) and Small (SMC) Magellanic Clouds, and the Magellanic Bridge (MBR). This system contains a diverse sample of star clusters. Their parameters, such as the spatial distribution, chemical composition and age distribution yield important information about the formation scenario of the whole Magellanic System. Using deep photometric maps compiled in the fourth phase of the Optical Gravitational Lensing Experiment (OGLE-IV) we present the most complete catalog of star clusters in the Magellanic System ever constructed from homogeneous, long time-scale photometric data. In this second paper of the series, we show the collection of star clusters found in the area of about 360 square degrees in the MBR and in the outer regions of the SMC. Our sample contains 198 visually identified star cluster candidates, 75 of which were not listed in any of the previously published catalogs. The new discoveries are mainly young small open clusters or clusters similar to associations.

Chemical study of the metal-rich globular cluster NGC 5927

NASA Astrophysics Data System (ADS)

Mura-Guzmán, A.; Villanova, S.; Muñoz, C.; Tang, B.

2018-03-01

Globular clusters (GCs) are natural laboratories where stellar and chemical evolution can be studied in detail. In addition, their chemical patterns and kinematics can tell us to which Galactic structure (disc, bulge, halo or extragalactic) the cluster belongs to. NGC 5927 is one of most metal-rich GCs in the Galaxy and its kinematics links it to the thick disc. We present abundance analysis based on high-resolution spectra of seven giant stars. The data were obtained using Fibre Large Array Multi Element Spectrograph/Ultraviolet Echelle Spectrograph (UVES) spectrograph mounted on UT2 telescope of the European Southern Observatory. The principal objective of this work is to perform a wide and detailed chemical abundance analysis of the cluster and look for possible Multiple Populations (MPs). We determined stellar parameters and measured 22 elements corresponding to light (Na, Al), alpha (O, Mg, Si, Ca, Ti), iron-peak (Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn), and heavy elements (Y, Zr, Ba, Ce, Nd, Eu). We found a mean iron content of [Fe/H] = -0.47 ± 0.02 (error on the mean). We confirm the existence of MPs in this GC with an O-Na anti-correlation, and moderate spread in Al abundances. We estimate a mean [α/Fe] = 0.25 ± 0.08. Iron-peak elements show no significant spread. The [Ba/Eu] ratios indicate a predominant contribution from SNeII for the formation of the cluster.

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.

Age and metallicity effects in single stellar populations: application to M 31 clusters.

NASA Astrophysics Data System (ADS)

de Freitas Pacheco, J. A.

1997-03-01

We have recently calculated (Borges et al. 1995AJ....110.2408B) integrated metallicity indices for single stellar populations (SSP). Effects of age, metallicity and abundances were taken into account. In particular, the explicit dependence of the indices Mg_2_ and NaD respectively on the ratios [Mg/Fe] and [Na/Fe] was included in the calibration. We report in this work an application of those models to a sample of 12 globular clusters in M 31. A fitting procedure was used to obtain age, metallicity and the [Mg/Fe] ratio for each object, which best reproduce the data. The mean age of the sample is 15+/-2.8Gyr and the mean [Mg/Fe] ratio is 0.35+/-0.10. These values and the derived metallicity spread are comparable to those found in galactic counterparts.

Reversible redox and clusterization of silver in glasses by X-ray irradiation and heat treatment: Mechanism of photochromic behavior of halogen-free silver-doped glass

NASA Astrophysics Data System (ADS)

Isaji, Tomoya; Wakasugi, Takashi; Fukumi, Kohei; Kadono, Kohei

2012-01-01

We investigated photochromic behavior, i.e. X-ray irradiation and post-heat-treatment-induced reversible redox and clusterization reactions of silver, in soda-lime silicate (74SiO2·16Na2O·8CaO·2Al2O3) and aluminosilicate ((75 - x)SiO2·25Na2O·xAl2O3 (x = 5-25)) glasses. Generation and annihilation of silver nanoparticles were observed for soda-lime silicate and x = 5 aluminosilicate glasses doped with 0.05 wt.% or less of Ag while no nanoparticles were formed for x = 15-25 aluminosilicate glasses even doped with 0.5 wt.% of Ag. These results were analyzed from the viewpoints of the reaction kinetics and network structures of the glasses.

NaCl nucleation from brine in seeded simulations: Sources of uncertainty in rate estimates.

PubMed

Zimmermann, Nils E R; Vorselaars, Bart; Espinosa, Jorge R; Quigley, David; Smith, William R; Sanz, Eduardo; Vega, Carlos; Peters, Baron

2018-06-14

This work reexamines seeded simulation results for NaCl nucleation from a supersaturated aqueous solution at 298.15 K and 1 bar pressure. We present a linear regression approach for analyzing seeded simulation data that provides both nucleation rates and uncertainty estimates. Our results show that rates obtained from seeded simulations rely critically on a precise driving force for the model system. The driving force vs. solute concentration curve need not exactly reproduce that of the real system, but it should accurately describe the thermodynamic properties of the model system. We also show that rate estimates depend strongly on the nucleus size metric. We show that the rate estimates systematically increase as more stringent local order parameters are used to count members of a cluster and provide tentative suggestions for appropriate clustering criteria.

Ionic Vapor Composition in Critical and Supercritical States of Strongly Interacting Ionic Compounds.

PubMed

Chaban, Vitaly V; Prezhdo, Oleg V

2016-05-12

The critical point, CP (T, P), of the phase diagram quantifies the minimum amount of kinetic energy needed to prevent a substance from existing in a condensed phase. Therefore, the CP is closely related to the properties of the fluid far below the critical temperature. Approaches designed to predict thermophysical properties of a system necessarily aim to provide reliable estimates of the CP. Vice versa, CP estimation is impossible without knowledge of the vapor phase behavior. We report ab initio Born-Oppenheimer molecular dynamics (BOMD) simulations of sodium and potassium chlorides, NaCl and KCl, at and above their expected CPs. We advance the present knowledge regarding the existence of ionic species in the vapor phase by establishing significant percentages of atomic clusters: 29-30% in NaCl and 34-38% in KCl. A neutral pair of counterions is the most abundant cluster in the ionic vapors (ca. 35% of all vaporized ions exist in this form). Unexpectedly, an appreciable fraction of clusters is charged. The ionic vapor composition is determined by the vapor density, rather than the nature of the alkali ion. The previously suggested CPs of NaCl and KCl appear overestimated, based on the present simulations. The reported results offer essential insights into the ionic fluid properties and assist in development of thermodynamic theories. The ab initio BOMD method has been applied to investigate the vapor phase composition of an ionic fluid for the first time.

Alkali-ion microsolvation with benzene molecules.

PubMed

Marques, J M C; Llanio-Trujillo, J L; Albertí, M; Aguilar, A; Pirani, F

2012-05-24

The target of this investigation is to characterize by a recently developed methodology, the main features of the first solvation shells of alkaline ions in nonpolar environments due to aromatic rings, which is of crucial relevance to understand the selectivity of several biochemical phenomena. We employ an evolutionary algorithm to obtain putative global minima of clusters formed with alkali-ions (M(+)) solvated with n benzene (Bz) molecules, i.e., M(+)-(Bz)(n). The global intermolecular interaction has been decomposed in Bz-Bz and in M(+)-Bz contributions, using a potential model based on different decompositions of the molecular polarizability of benzene. Specifically, we have studied the microsolvation of Na(+), K(+), and Cs(+) with benzene molecules. Microsolvation clusters up to n = 21 benzene molecules are involved in this work and the achieved global minimum structures are reported and discussed in detail. We observe that the number of benzene molecules allocated in the first solvation shell increases with the size of the cation, showing three molecules for Na(+) and four for both K(+) and Cs(+). The structure of this solvation shell keeps approximately unchanged as more benzene molecules are added to the cluster, which is independent of the ion. Particularly stable structures, so-called "magic numbers", arise for various nuclearities of the three alkali-ions. Strong "magic numbers" appear at n = 2, 3, and 4 for Na(+), K(+), and Cs(+), respectively. In addition, another set of weaker "magic numbers" (three per alkali-ion) are reported for larger nuclearities.

Constraint shapes convergence in tetrodotoxin-resistant sodium channels of snakes.

PubMed

Feldman, Chris R; Brodie, Edmund D; Brodie, Edmund D; Pfrender, Michael E

2012-03-20

Natural selection often produces convergent changes in unrelated lineages, but the degree to which such adaptations occur via predictable genetic paths is unknown. If only a limited subset of possible mutations is fixed in independent lineages, then it is clear that constraint in the production or function of molecular variants is an important determinant of adaptation. We demonstrate remarkably constrained convergence during the evolution of resistance to the lethal poison, tetrodotoxin, in six snake species representing three distinct lineages from around the globe. Resistance-conferring amino acid substitutions in a voltage-gated sodium channel, Na(v)1.4, are clustered in only two regions of the protein, and a majority of the replacements are confined to the same three positions. The observed changes represent only a small fraction of the experimentally validated mutations known to increase Na(v)1.4 resistance to tetrodotoxin. These results suggest that constraints resulting from functional tradeoffs between ion channel function and toxin resistance led to predictable patterns of evolutionary convergence at the molecular level. Our data are consistent with theoretical predictions and recent microcosm work that suggest a predictable path is followed during an adaptive walk along a mutational landscape, and that natural selection may be frequently constrained to produce similar genetic outcomes even when operating on independent lineages.

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

Bragaglia, A.; Carretta, E.; Gratton, R. G.

We present the first chemical composition study of two unevolved stars in the globular cluster NGC 2808, obtained with the X-shooter spectrograph at VLT. NGC 2808 shows three discrete, well-separated main sequences. The most accepted explanation for this phenomenon is that their stars have different helium contents. We observed one star on the bluest main sequence (bMS, claimed to have a high helium content, Y {approx}0.4) and the other on the reddest main sequence (rMS, consistent with a canonical helium content, Y = 0.245). We analyzed features of NH, CH, Na, Mg, Al, and Fe. While Fe, Ca, and othermore » elements have the same abundances in the two stars, the bMS star shows a huge enhancement of N, a depletion of C, an enhancement of Na and Al, and a small depletion of Mg with respect to the rMS star. This is exactly what is expected if stars on the bMS formed from the ejecta produced by an earlier stellar generation in the complete CNO and MgAl cycles whose main product is helium. The elemental abundance pattern differences in these two stars are consistent with the differences in the helium content suggested by the color-magnitude diagram positions of the stars.« less

Global distribution of NA1 genotype of respiratory syncytial virus and its evolutionary dynamics assessed from the past 11 years.

PubMed

Haider, Md Shakir Hussain; Deeba, Farah; Khan, Wajihul Hasan; Naqvi, Irshad H; Ali, Sher; Ahmed, Anwar; Broor, Shobha; Alsenaidy, Hytham A; Alsenaidy, Abdulrahman M; Dohare, Ravins; Parveen, Shama

2018-06-01

Respiratory syncytial virus (RSV) is a potent pathogen having global distribution. The main purpose of this study was to gain an insight into distribution pattern of the NA1 genotype of group A RSV across the globe together with its evolutionary dynamics. We focused on the second hypervariable region of the G protein gene and used the same for Phylogenetic, Bayesian and Network analyses. Eighteen percent of the samples collected from 500 symptomatic pediatric patients with acute respiratory tract infection (ARI) were found to be positive for RSV during 2011-15 from New Delhi, India. Of these, group B RSV was predominant and clustered into two different genotypes (BA and SAB4). Similarly, group A viruses clustered into two genotypes (NA1 and ON1). The data set from the group A viruses included 543 sequences from 23 different countries including 67 strains from India. The local evolutionary dynamics suggested consistent virus population of NA1 genotype in India during 2009 to 2014. The molecular clock analysis suggested that most recent common ancestor of group A and NA1 genotype have emerged in during the years 1953 and 2000, respectively. The global evolutionary rates of group A viruses and NA1 genotype were estimated to be 3.49 × 10 -3 (95% HPD, 2.90-4.17 × 10 -3 ) and 3.56 × 10 -3 (95% HPD, 2.91 × 10 -3 -4.18 × 10 -3 ) substitution/site/year, respectively. Analysis of the NA1 genotype of group A RSV reported during 11 years i.e. from 2004 to 2014 showed its dominance in 21 different countries across the globe reflecting its evolutionary dynamics. The Network analysis showed highly intricate but an inconsistent pattern of haplotypes of NA1 genotype circulating in the world. Present study seems to be first comprehensive attempt on global distribution and evolution of NA1 genotype augmenting the optimism towards the vaccine development. Copyright © 2018 Elsevier B.V. All rights reserved.

Effect of dose and size on defect engineering in carbon cluster implanted silicon wafers

NASA Astrophysics Data System (ADS)

Okuyama, Ryosuke; Masada, Ayumi; Shigematsu, Satoshi; Kadono, Takeshi; Hirose, Ryo; Koga, Yoshihiro; Okuda, Hidehiko; Kurita, Kazunari

2018-01-01

Carbon-cluster-ion-implanted defects were investigated by high-resolution cross-sectional transmission electron microscopy toward achieving high-performance CMOS image sensors. We revealed that implantation damage formation in the silicon wafer bulk significantly differs between carbon-cluster and monomer ions after implantation. After epitaxial growth, small and large defects were observed in the implanted region of carbon clusters. The electron diffraction pattern of both small and large defects exhibits that from bulk crystalline silicon in the implanted region. On the one hand, we assumed that the silicon carbide structure was not formed in the implanted region, and small defects formed because of the complex of carbon and interstitial silicon. On the other hand, large defects were hypothesized to originate from the recrystallization of the amorphous layer formed by high-dose carbon-cluster implantation. These defects are considered to contribute to the powerful gettering capability required for high-performance CMOS image sensors.

Euchromatic Transposon Insertions Trigger Production of Novel Pi- and Endo-siRNAs at the Target Sites in the Drosophila Germline

PubMed Central

Olovnikov, Ivan; Abramov, Yuri; Kalmykova, Alla

2014-01-01

The control of transposable element (TE) activity in germ cells provides genome integrity over generations. A distinct small RNA–mediated pathway utilizing Piwi-interacting RNAs (piRNAs) suppresses TE expression in gonads of metazoans. In the fly, primary piRNAs derive from so-called piRNA clusters, which are enriched in damaged repeated sequences. These piRNAs launch a cycle of TE and piRNA cluster transcript cleavages resulting in the amplification of piRNA and TE silencing. Using genome-wide comparison of TE insertions and ovarian small RNA libraries from two Drosophila strains, we found that individual TEs inserted into euchromatic loci form novel dual-stranded piRNA clusters. Formation of the piRNA-generating loci by active individual TEs provides a more potent silencing response to the TE expansion. Like all piRNA clusters, individual TEs are also capable of triggering the production of endogenous small interfering (endo-si) RNAs. Small RNA production by individual TEs spreads into the flanking genomic regions including coding cellular genes. We show that formation of TE-associated small RNA clusters can down-regulate expression of nearby genes in ovaries. Integration of TEs into the 3′ untranslated region of actively transcribed genes induces piRNA production towards the 3′-end of transcripts, causing the appearance of genic piRNA clusters, a phenomenon that has been reported in different organisms. These data suggest a significant role of TE-associated small RNAs in the evolution of regulatory networks in the germline. PMID:24516406

Multilevel analyses of SCN5A mutations in arrhythmogenic right ventricular dysplasia/cardiomyopathy suggest non-canonical mechanisms for disease pathogenesis.

PubMed

Te Riele, Anneline S J M; Agullo-Pascual, Esperanza; James, Cynthia A; Leo-Macias, Alejandra; Cerrone, Marina; Zhang, Mingliang; Lin, Xianming; Lin, Bin; Sobreira, Nara L; Amat-Alarcon, Nuria; Marsman, Roos F; Murray, Brittney; Tichnell, Crystal; van der Heijden, Jeroen F; Dooijes, Dennis; van Veen, Toon A B; Tandri, Harikrishna; Fowler, Steven J; Hauer, Richard N W; Tomaselli, Gordon; van den Berg, Maarten P; Taylor, Matthew R G; Brun, Francesca; Sinagra, Gianfranco; Wilde, Arthur A M; Mestroni, Luisa; Bezzina, Connie R; Calkins, Hugh; Peter van Tintelen, J; Bu, Lei; Delmar, Mario; Judge, Daniel P

2017-01-01

Arrhythmogenic Right Ventricular Dysplasia/Cardiomyopathy (ARVD/C) is often associated with desmosomal mutations. Recent studies suggest an interaction between the desmosome and sodium channel protein Na v 1.5. We aimed to determine the prevalence and biophysical properties of mutations in SCN5A (the gene encoding Na v 1.5) in ARVD/C. We performed whole-exome sequencing in six ARVD/C patients (33% male, 38.2 ± 12.1 years) without a desmosomal mutation. We found a rare missense variant (p.Arg1898His; R1898H) in SCN5A in one patient. We generated induced pluripotent stem cell-derived cardiomyocytes (hIPSC-CMs) from the patient's peripheral blood mononuclear cells. The variant was then corrected (R1898R) using Clustered Regularly Interspaced Short Palindromic Repeats/Cas9 technology, allowing us to study the impact of the R1898H substitution in the same cellular background. Whole-cell patch clamping revealed a 36% reduction in peak sodium current (P = 0.002); super-resolution fluorescence microscopy showed reduced abundance of Na V 1.5 (P = 0.005) and N-Cadherin (P = 0.026) clusters at the intercalated disc. Subsequently, we sequenced SCN5A in an additional 281 ARVD/C patients (60% male, 34.8 ± 13.7 years, 52% desmosomal mutation-carriers). Five (1.8%) subjects harboured a putatively pathogenic SCN5A variant (p.Tyr416Cys, p.Leu729del, p.Arg1623Ter, p.Ser1787Asn, and p.Val2016Met). SCN5A variants were associated with prolonged QRS duration (119 ± 15 vs. 94 ± 14 ms, P < 0.01) and all SCN5A variant carriers had major structural abnormalities on cardiac imaging. Almost 2% of ARVD/C patients harbour rare SCN5A variants. For one of these variants, we demonstrated reduced sodium current, Na v 1.5 and N-Cadherin clusters at junctional sites. This suggests that Na v 1.5 is in a functional complex with adhesion molecules, and reveals potential non-canonical mechanisms by which Na v 1.5 dysfunction causes cardiomyopathy. Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2016. For permissions, please email: journals.permissions@oup.com.

Effect of Intravenous Small-Volume Hypertonic Sodium Bicarbonate, Sodium Chloride, and Glucose Solutions in Decreasing Plasma Potassium Concentration in Hyperkalemic Neonatal Calves with Diarrhea.

PubMed

Trefz, F M; Constable, P D; Lorenz, I

2017-05-01

Hyperkalemia is a frequently observed electrolyte imbalance in dehydrated neonatal diarrheic calves that can result in skeletal muscle weakness and life-threatening cardiac conduction abnormalities and arrhythmias. Intravenous administration of a small-volume hypertonic NaHCO 3 solution is clinically more effective in decreasing the plasma potassium concentration (cK) in hyperkalemic diarrheic calves than hypertonic NaCl or glucose solutions. Twenty-two neonatal diarrheic calves with cK >5.8 mmol/L. Prospective randomized clinical trial. Calves randomly received either 8.4% NaHCO 3 (6.4 mL/kg BW; n = 7), 7.5% NaCl (5 mL/kg BW; n = 8), or 46.2% glucose (5 mL/kg BW; n = 7) IV over 5 minutes and were subsequently allowed to suckle 2 L of an electrolyte solution. Infusions with NaHCO 3 and NaCl provided an identical sodium load of 6.4 mmol/kg BW. Hypertonic NaHCO 3 infusions produced an immediate and sustained decrease in plasma cK. Hypertonic glucose infusions resulted in marked hyperglycemia and hyperinsulinemia, but cK remained unchanged for 20 minutes. Between 30 and 120 minutes after initiation of treatment, the most marked decrements in cK from baseline occurred in group NaHCO 3 , which were significantly (P < .05) larger during this period of time than in calves in group NaCl, but not group glucose. After 120 minutes, the mean decrease in cK from baseline was -26 ± 10%, -9 ± 8%, and -22 ± 6% in groups NaHCO 3 , NaCl, and glucose, respectively. Small-volume hypertonic NaHCO 3 infusions appear to have clinical advantages for the rapid resuscitation of hyperkalemic diarrheic calves, compared to hypertonic NaCl or glucose solutions. Copyright © 2017 The Authors. Journal of Veterinary Internal Medicine published by Wiley Periodicals, Inc. on behalf of the American College of Veterinary Internal Medicine.

Kinetics of Aggregation with Choice

DOE PAGES

Ben-Naim, Eli; Krapivsky, Paul

2016-12-01

Here we generalize the ordinary aggregation process to allow for choice. In ordinary aggregation, two random clusters merge and form a larger aggregate. In our implementation of choice, a target cluster and two candidate clusters are randomly selected and the target cluster merges with the larger of the two candidate clusters.We study the long-time asymptotic behavior and find that as in ordinary aggregation, the size density adheres to the standard scaling form. However, aggregation with choice exhibits a number of different features. First, the density of the smallest clusters exhibits anomalous scaling. Second, both the small-size and the large-size tailsmore » of the density are overpopulated, at the expense of the density of moderate-size clusters. Finally, we also study the complementary case where the smaller candidate cluster participates in the aggregation process and find an abundance of moderate clusters at the expense of small and large clusters. Additionally, we investigate aggregation processes with choice among multiple candidate clusters and a symmetric implementation where the choice is between two pairs of clusters.« less

OGLE Collection of Star Clusters. New Objects in the Outskirts of the Large Magellanic Cloud

NASA Astrophysics Data System (ADS)

Sitek, M.; Szymański, M. K.; Skowron, D. M.; Udalski, A.; Kostrzewa-Rutkowska, Z.; Skowron, J.; Karczmarek, P.; Cieślar, M.; Wyrzykowski, Ł.; Kozłowski, S.; Pietrukowicz, P.; Soszyński, I.; Mróz, P.; Pawlak, M.; Poleski, R.; Ulaczyk, K.

2016-09-01

The Magellanic System (MS), consisting of the Large Magellanic Cloud (LMC), the Small Magellanic Cloud (SMC) and the Magellanic Bridge (MBR), contains diverse sample of star clusters. Their spatial distribution, ages and chemical abundances may provide important information about the history of formation of the whole System. We use deep photometric maps derived from the images collected during the fourth phase of the Optical Gravitational Lensing Experiment (OGLE-IV) to construct the most complete catalog of star clusters in the Large Magellanic Cloud using the homogeneous photometric data. In this paper we present the collection of star clusters found in the area of about 225 square degrees in the outer regions of the LMC. Our sample contains 679 visually identified star cluster candidates, 226 of which were not listed in any of the previously published catalogs. The new clusters are mainly young small open clusters or clusters similar to associations.

Investigation of Metal and Metal Oxide Clusters Small Enough to Constitute the Critical Size for Gas Phase Nucleation in Combustion Processes.

DTIC Science & Technology

1980-11-01

Ao-A093 950 NORTHWESTERN UNIV EVANSTON IL DEPT OF M4ECHANICAL ND-ETC F/S 7/4 INVESTIGATION OF 1ETAL AND METAL OXIDE CLUSTERS S1ALL ENOUGH TO--ETC(U...34 " 18. SUPPLEMENTARY NOTES 19. KEY WORDS (Continue on reveroe side if necessary snd Identify by block number) Clusters , Nucleation, Molecular Beam, Free...contract a variety of techniques have been employed to study the properties of small atomic and molecular clusters formed in the gas phase via

Ultra-small rhenium clusters supported on graphene.

PubMed

Miramontes, Orlando; Bonafé, Franco; Santiago, Ulises; Larios-Rodriguez, Eduardo; Velázquez-Salazar, Jesús J; Mariscal, Marcelo M; Yacaman, Miguel José

2015-03-28

The adsorption of very small rhenium clusters (2-13 atoms) supported on graphene was studied by high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM). The atomic structure of the clusters was fully resolved with the aid of density functional theory calculations and STEM simulations. It was found that octahedral and tetrahedral structures work as seeds to obtain more complex morphologies. Finally, a detailed analysis of the electronic structure suggested that a higher catalytic effect can be expected in Re clusters when adsorbed on graphene than in isolated ones.

Ultra-small rhenium clusters supported on graphene

PubMed Central

Miramontes, Orlando; Bonafé, Franco; Santiago, Ulises; Larios-Rodriguez, Eduardo; Velázquez-Salazar, Jesús J.; Mariscal, Marcelo M.; Yacaman, Miguel José

2015-01-01

The adsorption of very small rhenium clusters (2 – 13 atoms) supported on graphene was studied with high annular dark field - scanning transmission electron microscopy (HAADF-STEM). The atomic structure of the clusters was fully resolved with the aid of density functional calculations and STEM simulations. It was found that octahedral and tetrahedral structures work as seeds to obtain more complex morphologies. Finally, a detailed analysis of the electronic structure suggested that a higher catalytic effect can be expected in Re clusters when adsorbed on graphene than in isolated ones. PMID:25721176

Fixation of CO2 in bi-layered coordination networks of zinc tetra(4-carboxyphenyl)porphyrin with multi-component [Pr2Na3(NO3)(H2O)3] connectors.

PubMed

Nandi, Goutam; Goldberg, Israel

2014-11-14

CO2 is fixed in a rare μ2-η bridging mode by bi-layered coordination networks of ZnTCPP tessellated along the four equatorial directions by [Pr2Na3(NO3)(H2O)3](8+) connecting clusters in a 2 : 1 ratio (1), but not in the isomorphous free-base porphyrin analogue [(TCPPH2)2(Pr2Na3(NO3)(H2O)3)]n (2), revealing the crucial role of the zinc metal in this process.

Responses of primate cortical neurons to unitary and binary taste stimuli.

PubMed

Miyaoka, Y; Pritchard, T C

1996-01-01

1. The responses of 126 neurons in primary gustatory cortices of two rhesus monkeys were recorded during sapid stimulation of the tongue with 18 taste stimuli. Ten of these stimuli were dissolved in distilled water (DW): 1.0 M sucrose (Suc), 0.1 M and 0.03 M sodium chloride (NaCl), 0.003 M hydrochloric acid (HCl), 0.001 M quinine hydrochloride (QHCl), 0.03 M monosodium glutamate (MSG), 0.03 M polycose, 0.3 M glycine, 0.1 M proline, and 0.1 M malic acid. Seven other stimuli were dissolved in 0.03 M MSG; the last stimulus was a mixture of 1.0 M Suc and 0.03 M NaCl. 2. The average spontaneous rate (2.2 +/- 0.2 spikes/s, mean +/- SE) and response to DW (2.5 +/- 0.2) of these 126 neurons was low but within the range previously reported for neurons in primate taste cortex. Suc was the most effective stimulus for 24.1% of the neurons tested followed by NaCl (15.7%), QHCl (14.8%), HCl (11.1%), MSG (10.2%), and other miscellaneous unitary gustatory stimuli (8.3%). Binary taste mixtures were the most effective stimuli for 15.7% of the sample. The net responses (corrected for DW, in spikes/s) for Suc-best (3.3), NaCl-best (4.3), HCl-best (3.4), QHCl-best (2.3), and MSG-best (4.1) were sluggish, but comparable with that reported previously. 3. The response breadth of the 82 neurons that responded best to either Suc, NaCl, HCl, or QHCl measured with the entropy coefficient indicated a moderate response breadth for these neurons (mean = 0.79; range = 0.30-0.98). According to the response criteria adopted in this experiment (water response +/- 1.96 SD), however, 81 of these 82 neurons (98.1%) responded to only one or two of the four basic taste stimuli. The disparity between the entropy- and criterion-based measures of response derive from the nature of the two statistics. Adjustments that would make the entropy statistic less inclusive and the definition of a response according to statistical criteria less exclusive would increase their concordance. 4. Three multivariate statistics (cluster, principal axis factor, and multidimensional analysis) were used to analyze the data. Cluster analysis enabled us to divide the 82 taste neurons into groups on the basis of response similarity. Each of the four largest groups was dominated by neurons that responded best to one of the four basic taste stimuli: Suc, NaCl, QHCl, and HCl (ranked in descending order); the fifth largest cluster contained neurons that responded best to MSG. Principal axis factor analysis demonstrated that 80.8% of the total variance could be accounted for by three factors. Neurons responding best to Suc, NaCl, and QHCl each were closely associated with one of those three factors, but the loadings of the HCl-best neurons were evenly distributed across all three factors. The communality coefficient of these three factors was > 80% for the Suc-, NaCl-, HCl-, and QHCl-best neurons; the MSG-best neurons, by comparison, had very few high loadings on any of these three factors and a correspondingly low communality coefficient of 40.4%, a difference that was statistically significant from the other four groups. Thus the three factors related to Suc-, NaCl-, HCl-, and QHCl-best neurons are not relevant to MSG-best neurons. We used multidimensional analysis to arrange the neurons that responded best to Suc, NaCl, HCl, QHCl, and MSG into five loosely arranged and partially overlapping clusters. A multidimensional space based on stimulus similarity showed that MSG was as different from the four basic taste stimuli as they were from one another. 5. Mixture suppression, a common observation in human psychophysical experiments, was examined at the neurophysiological level by including binary tastants in the stimulus battery. The average response of 19 Suc-best neurons to 1.0 M Suc (4.1 spikes/s) decreased to near 0 when the solvent was changed from DW to either 0.03 M MSG or 0.03 M NaCl. Similar decrements were observed in NaCl- and MSG-best neurons tested with Suc/NaCl mixtures.

Perception of aesthetics and personality traits in orthognathic surgery patients: A comparison of still and moving images

PubMed Central

Tran, Ulrich S.; Wutzl, Arno; Seemann, Rudolf; Millesi, Gabriele; Jagsch, Reinhold

2018-01-01

It is common in practicing orthognathic surgery to evaluate faces with retruded or protruded chins (dysgnathic faces) using photographs. Because motion may alter how the face is perceived, we investigated the perception of faces presented via photographs and videos. Two hundred naïve raters (lay persons, without maxillo facial surgery background) evaluated 12 subjects with varying chin anatomy [so-called skeletal Class I (normal chin), Class II (retruded chin), and Class III (protruded chin)]. Starting from eight traits, with Factor analysis we found a two-Factor solution, i.e. an "aesthetics associated traits cluster" and a Factor "personality traits cluster" which appeared to be uncorrelated. Internal consistency of the Factors found for photographs and videos was excellent. Generally, female raters delivered better ratings than males, but the effect sizes were small. We analyzed differences and the respective effect magnitude between photograph and video perception. For each skeletal class the aesthetics associated dimensions were rated similarly between photographs and video clips. In contrast, specific personality traits were rated differently. Differences in the class-specific personality traits seen on photographs were "smoothed" in the assessment of videos, which implies that photos enhance stereotypes commonly attributed to a retruded or protruded chin. PMID:29775466

Wavelet investigation of preferential concentration in particle-laden turbulence

NASA Astrophysics Data System (ADS)

Bassenne, Maxime; Urzay, Javier; Schneider, Kai; Moin, Parviz

2017-11-01

Direct numerical simulations of particle-laden homogeneous-isotropic turbulence are employed in conjunction with wavelet multi-resolution analyses to study preferential concentration in both physical and spectral spaces. Spatially-localized energy spectra for velocity, vorticity and particle-number density are computed, along with their spatial fluctuations that enable the quantification of scale-dependent probability density functions, intermittency and inter-phase conditional statistics. The main result is that particles are found in regions of lower turbulence spectral energy than the corresponding mean. This suggests that modeling the subgrid-scale turbulence intermittency is required for capturing the small-scale statistics of preferential concentration in large-eddy simulations. Additionally, a method is defined that decomposes a particle number-density field into the sum of a coherent and an incoherent components. The coherent component representing the clusters can be sparsely described by at most 1.6% of the total number of wavelet coefficients. An application of the method, motivated by radiative-heat-transfer simulations, is illustrated in the form of a grid-adaptation algorithm that results in non-uniform meshes refined around particle clusters. It leads to a reduction of the number of control volumes by one to two orders of magnitude. PSAAP-II Center at Stanford (Grant DE-NA0002373).

Classification of stellar populations in globular clusters

NASA Astrophysics Data System (ADS)

Wang, Yue; Zhao, Gang; Li, Hai-Ning

2017-04-01

Possessing multiple stellar populations has been accepted as a common feature of globular clusters (GCs). Different stellar populations manifest themselves with different chemical features, e.g. the well-known O-Na anti-correlation. Generally, the first (primordial) population has O and Na abundances consistent with those of field stars with similar metallicity; while the second (polluted) population is identified by their Na overabundance and O deficiency. The fraction of the populations is an important constraint on the GC formation scenario. Several methods have been proposed for the classification of GC populations. Here we examine a criterion derived based on the distribution of Galactic field stars, which relies on Na abundance as a function of [Fe/H], to distinguish first and second stellar populations in GCs. By comparing the first population fractions of 17 GCs estimated by the field star criterion with those in the literature derived by methods related to individual GCs, we find that the field star criterion tends to overestimate the first population fractions. The population separation methods, which are related to an individual GC sample, are recommended because the diversity of GCs can be taken into consideration. Currently, more caution should be exercised if one wants to regard field stars as a reference for the identification of a GC population. However, further study on the connection between field stars and GCs populations is still needed.

Transient regulation of three clustered tomato class-I small heat-shock chaperone genes by ethylene is mediated by SIMADS-RIN transcription factor

USDA-ARS?s Scientific Manuscript database

An intronless cluster of three class I small heat shock protein (sHSP) chaperone genes, Sl17.6, Sl20.0 and Sl20.1, resident on the short arm of chromosome 6 in tomato, was previously characterized (Goyal et al., 2012). This shsp chaperone gene cluster was found decorated with cis sequences known to ...

A MicroRNA Cluster miR-23-24-27 Is Upregulated by Aldosterone in the Distal Kidney Nephron Where it Alters Sodium Transport.

PubMed

Liu, Xiaoning; Edinger, Robert S; Klemens, Christine A; Phua, Yu L; Bodnar, Andrew J; LaFramboise, William A; Ho, Jacqueline; Butterworth, Michael B

2017-06-01

The epithelial sodium channel (ENaC) is expressed in the epithelial cells of the distal convoluted tubules, connecting tubules, and cortical collecting duct (CCD) in the kidney nephron. Under the regulation of the steroid hormone aldosterone, ENaC is a major determinant of sodium (Na + ) and water balance. The ability of aldosterone to regulate microRNAs (miRs) in the kidney has recently been realized, but the role of miRs in Na + regulation has not been well established. Here we demonstrate that expression of a miR cluster mmu-miR-23-24-27, is upregulated in the CCD by aldosterone stimulation both in vitro and in vivo. Increasing the expression of these miRs increased Na + transport in the absence of aldosterone stimulation. Potential miR targets were evaluated and miR-27a/b was verified to bind to the 3'-untranslated region of intersectin-2, a multi-domain protein expressed in the distal kidney nephron and involved in the regulation of membrane trafficking. Expression of Itsn2 mRNA and protein was decreased after aldosterone stimulation. Depletion of Itsn2 expression, mimicking aldosterone regulation, increased ENaC-mediated Na + transport, while Itsn2 overexpression reduced ENaC's function. These findings reinforce a role for miRs in aldosterone regulation of Na + transport, and implicate miR-27 in aldosterone's action via a novel target. J. Cell. Physiol. 232: 1306-1317, 2017. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

Quasi-planar elemental clusters in pair interactions approximation

NASA Astrophysics Data System (ADS)

Chkhartishvili, Levan

2016-01-01

The pair-interactions approximation, when applied to describe elemental clusters, only takes into account bonding between neighboring atoms. According to this approach, isomers of wrapped forms of 2D clusters - nanotubular and fullerene-like structures - and truly 3D clusters, are generally expected to be more stable than their quasi-planar counterparts. This is because quasi-planar clusters contain more peripheral atoms with dangling bonds and, correspondingly, fewer atoms with saturated bonds. However, the differences in coordination numbers between central and peripheral atoms lead to the polarization of bonds. The related corrections to the molar binding energy can make small, quasi-planar clusters more stable than their 2D wrapped allotropes and 3D isomers. The present work provides a general theoretical frame for studying the relative stability of small elemental clusters within the pair interactions approximation.

Low-temperature glasslike properties in (NaCl)1-x(NaCN)x

NASA Astrophysics Data System (ADS)

Watson, Susan K.; Pohl, R. O.

1995-04-01

Thermal conductivity, internal friction, transverse sound velocity (60 mK to 300 K), and specific-heat data (100 mK to 40 K) for (NaCl)1-x(NaCN)x (x=0, 0.025, 0.05, 0.1, 0.76, 1) show a progression from crystalline to glasslike behavior as the CN- concentration is increased from 0 to 76 %. The evolution of glasslike properties is compared to that in other crystals in which glasslike properties evolve with increasing disorder, e.g., (KBr)1-x(KCN)x and Ba1-xLaxF2-x. For (KBr)1-x(KCN)x, Sethna and Chow have shown that as the concentration of the almost freely rotating CN- ions is increased the average potential barrier for CN- reorientation also increases through elastic quadrupolar interactions. For x~0.5, only a small density of low-energy states is left, which equals that observed in structural glasses. In Ba1-xLaxF2-x, on the other hand, the crystal field for small doping x is so large that no atomic motion occurs at low temperatures. (NaCl)1-x(NaCN)x is shown to represent an intermediate case, in that the crystal field is non-negligible at small x, yet glasslike low-energy excitations indicative of very small potential barrier heights evolve with increasing x. It is argued that random internal strains cause a decrease of the barrier heights in these crystals, which lead to the low-energy excitations. It is proposed that random strains have a similar effect in other disordered crystals as in Ba1-xLaxF2-x, which for small x show no low-energy mobile states, yet which for large x become glasslike.

Myeloid Clusters Are Associated with a Pro-Metastatic Environment and Poor Prognosis in Smoking-Related Early Stage Non-Small Cell Lung Cancer

PubMed Central

Zhang, Wang; Pal, Sumanta K.; Liu, Xueli; Yang, Chunmei; Allahabadi, Sachin; Bhanji, Shaira; Figlin, Robert A.; Yu, Hua; Reckamp, Karen L.

2013-01-01

Background This study aimed to understand the role of myeloid cell clusters in uninvolved regional lymph nodes from early stage non-small cell lung cancer patients. Methods Uninvolved regional lymph node sections from 67 patients with stage I–III resected non-small cell lung cancer were immunostained to detect myeloid clusters, STAT3 activity and occult metastasis. Anthracosis intensity, myeloid cluster infiltration associated with anthracosis and pSTAT3 level were scored and correlated with patient survival. Multivariate Cox regression analysis was performed with prognostic variables. Human macrophages were used for in vitro nicotine treatment. Results CD68+ myeloid clusters associated with anthracosis and with an immunosuppressive and metastasis-promoting phenotype and elevated overall STAT3 activity were observed in uninvolved lymph nodes. In patients with a smoking history, myeloid cluster score significantly correlated with anthracosis intensity and pSTAT3 level (P<0.01). Nicotine activated STAT3 in macrophages in long-term culture. CD68+ myeloid clusters correlated and colocalized with occult metastasis. Myeloid cluster score was an independent prognostic factor (P = 0.049) and was associated with survival by Kaplan-Maier estimate in patients with a history of smoking (P = 0.055). The combination of myeloid cluster score with either lymph node stage or pSTAT3 level defined two populations with a significant difference in survival (P = 0.024 and P = 0.004, respectively). Conclusions Myeloid clusters facilitate a pro-metastatic microenvironment in uninvolved regional lymph nodes and associate with occult metastasis in early stage non-small cell lung cancer. Myeloid cluster score is an independent prognostic factor for survival in patients with a history of smoking, and may present a novel method to inform therapy choices in the adjuvant setting. Further validation studies are warranted. PMID:23717691

First-principles investigation of the dissociation and coupling of methane on small copper clusters: Interplay of collision dynamics and geometric and electronic effects

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

Varghese, Jithin J.; Mushrif, Samir H., E-mail: shmushrif@ntu.edu.sg

Small metal clusters exhibit unique size and morphology dependent catalytic activity. The search for alternate minimum energy pathways and catalysts to transform methane to more useful chemicals and carbon nanomaterials led us to investigate collision induced dissociation of methane on small Cu clusters. We report here for the first time, the free energy barriers for the collision induced activation, dissociation, and coupling of methane on small Cu clusters (Cu{sub n} where n = 2–12) using ab initio molecular dynamics and metadynamics simulations. The collision induced activation of the stretching and bending vibrations of methane significantly reduces the free energy barriermore » for its dissociation. Increase in the cluster size reduces the barrier for dissociation of methane due to the corresponding increase in delocalisation of electron density within the cluster, as demonstrated using the electron localisation function topology analysis. This enables higher probability of favourable alignment of the C–H stretching vibration of methane towards regions of high electron density within the cluster and makes higher number of sites available for the chemisorption of CH{sub 3} and H upon dissociation. These characteristics contribute in lowering the barrier for dissociation of methane. Distortion and reorganisation of cluster geometry due to high temperature collision dynamics disturb electron delocalisation within them and increase the barrier for dissociation. Coupling reactions of CH{sub x} (x = 1–3) species and recombination of H with CH{sub x} have free energy barriers significantly lower than complete dehydrogenation of methane to carbon. Thus, competition favours the former reactions at high hydrogen saturation on the clusters.« less

Studies on the magnetic ground state of a spin Mobius strip

DOE PAGES

Newton, Graham N.; Hoshino, Norihisa; Matsumoto, Takuto; ...

2016-08-22

In this paper, we report the synthesis, structure and detailed characterisation of three n-membered oxovanadium rings, Na n[(V=O) nNa n(H 2O) n(α, β, or γ-CD) 2]•m H 2O (n=6, 7, or 8), prepared by the reactions of (V=O)SO 4•x H 2O with α, β, or γ-cyclodextrins (CDs) and NaOH in water. Their alternating heterometallic vanadium/sodium cyclic core structures were sandwiched between two CD moieties such that O-Na-O groups separated the neighbouring vanadyl ions. Antiferromagnetic interactions between the S=1/2 vanadyl ions led to S=0 ground states for the even-membered rings, but to two quasi-degenerate S=1/2 states for the spin-frustrated heptanuclear cluster.

Predicting vacancy-mediated diffusion of interstitial solutes in α -Fe

NASA Astrophysics Data System (ADS)

Barouh, Caroline; Schuler, Thomas; Fu, Chu-Chun; Jourdan, Thomas

2015-09-01

Based on a systematic first-principles study, the lowest-energy migration mechanisms and barriers for small vacancy-solute clusters (VnXm ) are determined in α -Fe for carbon, nitrogen, and oxygen, which are the most frequent interstitial solutes in several transition metals. We show that the dominant clusters present at thermal equilibrium (V X and V X2 ) have very reduced mobility compared to isolated solutes, while clusters composed of a solute bound to a small vacancy cluster may be significantly more mobile. In particular, V3X is found to be the fastest cluster for all three solutes. This result relies on the large diffusivity of the most compact trivacancy in a bcc lattice. Therefore, it may also be expected for interstitial solutes in other bcc metals. In the case of iron, we find that V3X may be as fast as or even more mobile than an interstitial solute. At variance with common assumptions, the trapping of interstitial solutes by vacancies does not necessarily decrease the mobility of the solute. Additionally, cluster dynamics simulations are performed considering a simple iron system with supersaturation of vacancies, in order to investigate the impacts of small mobile vacancy-solute clusters on properties such as the transport of solute and the cluster size distributions.

Influence of reactive gas admixture on transition metal cluster nucleation in a gas aggregation cluster source

NASA Astrophysics Data System (ADS)

Peter, Tilo; Polonskyi, Oleksandr; Gojdka, Björn; Mohammad Ahadi, Amir; Strunskus, Thomas; Zaporojtchenko, Vladimir; Biederman, Hynek; Faupel, Franz

2012-12-01

We quantitatively assessed the influence of reactive gases on the formation processes of transition metal clusters in a gas aggregation cluster source. A cluster source based on a 2 in. magnetron is used to study the production rate of titanium and cobalt clusters. Argon served as working gas for the DC magnetron discharge, and a small amount of reactive gas (oxygen and nitrogen) is added to promote reactive cluster formation. We found that the cluster production rate depends strongly on the reactive gas concentration for very small amounts of reactive gas (less than 0.1% of total working gas), and no cluster formation takes place in the absence of reactive species. The influence of discharge power, reactive gas concentration, and working gas pressure are investigated using a quartz micro balance in a time resolved manner. The strong influence of reactive gas is explained by a more efficient formation of nucleation seeds for metal-oxide or nitride than for pure metal.

Mass Distribution in Galaxy Cluster Cores

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

Hogan, M. T.; McNamara, B. R.; Pulido, F.

Many processes within galaxy clusters, such as those believed to govern the onset of thermally unstable cooling and active galactic nucleus feedback, are dependent upon local dynamical timescales. However, accurate mapping of the mass distribution within individual clusters is challenging, particularly toward cluster centers where the total mass budget has substantial radially dependent contributions from the stellar ( M {sub *}), gas ( M {sub gas}), and dark matter ( M {sub DM}) components. In this paper we use a small sample of galaxy clusters with deep Chandra observations and good ancillary tracers of their gravitating mass at both largemore » and small radii to develop a method for determining mass profiles that span a wide radial range and extend down into the central galaxy. We also consider potential observational pitfalls in understanding cooling in hot cluster atmospheres, and find tentative evidence for a relationship between the radial extent of cooling X-ray gas and nebular H α emission in cool-core clusters. At large radii the entropy profiles of our clusters agree with the baseline power law of K ∝ r {sup 1.1} expected from gravity alone. At smaller radii our entropy profiles become shallower but continue with a power law of the form K ∝ r {sup 0.67} down to our resolution limit. Among this small sample of cool-core clusters we therefore find no support for the existence of a central flat “entropy floor.”.« less

Small Sample Performance of Bias-corrected Sandwich Estimators for Cluster-Randomized Trials with Binary Outcomes

PubMed Central

Li, Peng; Redden, David T.

2014-01-01

SUMMARY The sandwich estimator in generalized estimating equations (GEE) approach underestimates the true variance in small samples and consequently results in inflated type I error rates in hypothesis testing. This fact limits the application of the GEE in cluster-randomized trials (CRTs) with few clusters. Under various CRT scenarios with correlated binary outcomes, we evaluate the small sample properties of the GEE Wald tests using bias-corrected sandwich estimators. Our results suggest that the GEE Wald z test should be avoided in the analyses of CRTs with few clusters even when bias-corrected sandwich estimators are used. With t-distribution approximation, the Kauermann and Carroll (KC)-correction can keep the test size to nominal levels even when the number of clusters is as low as 10, and is robust to the moderate variation of the cluster sizes. However, in cases with large variations in cluster sizes, the Fay and Graubard (FG)-correction should be used instead. Furthermore, we derive a formula to calculate the power and minimum total number of clusters one needs using the t test and KC-correction for the CRTs with binary outcomes. The power levels as predicted by the proposed formula agree well with the empirical powers from the simulations. The proposed methods are illustrated using real CRT data. We conclude that with appropriate control of type I error rates under small sample sizes, we recommend the use of GEE approach in CRTs with binary outcomes due to fewer assumptions and robustness to the misspecification of the covariance structure. PMID:25345738

Focus-based filtering + clustering technique for power-law networks with small world phenomenon

NASA Astrophysics Data System (ADS)

Boutin, François; Thièvre, Jérôme; Hascoët, Mountaz

2006-01-01

Realistic interaction networks usually present two main properties: a power-law degree distribution and a small world behavior. Few nodes are linked to many nodes and adjacent nodes are likely to share common neighbors. Moreover, graph structure usually presents a dense core that is difficult to explore with classical filtering and clustering techniques. In this paper, we propose a new filtering technique accounting for a user-focus. This technique extracts a tree-like graph with also power-law degree distribution and small world behavior. Resulting structure is easily drawn with classical force-directed drawing algorithms. It is also quickly clustered and displayed into a multi-level silhouette tree (MuSi-Tree) from any user-focus. We built a new graph filtering + clustering + drawing API and report a case study.

Chemical abundances of globular clusters in NGC 5128 (Centaurus A)

NASA Astrophysics Data System (ADS)

Hernandez, Svea; Larsen, Søren; Trager, Scott; Kaper, Lex; Groot, Paul

2018-06-01

We perform a detailed abundance analysis on integrated-light spectra of 20 globular clusters (GCs) in the early-type galaxy NGC 5128 (Centaurus A). The GCs were observed with X-Shooter on the Very Large Telescope (VLT). The cluster sample spans a metallicity range of -1.92 < [Fe/H] < -0.13 dex. Using theoretical isochrones, we compute synthetic integrated-light spectra and iterate the individual abundances until the best fit to the observations is obtained. We measured abundances of Mg, Ca, and Ti, and find a slightly higher enhancement in NGC 5128 GCs with metallicities [Fe/H] < -0.75 dex, of the order of ˜0.1 dex, than in the average values observed in the Milky Way (MW) for GCs of the same metallicity. If this α-enhancement in the metal-poor GCs in NGC 5128 is genuine, it could hint at a chemical enrichment history different than that experienced by the MW. We also measure Na abundances in 9 out of 20 GCs. We find evidence for intracluster abundance variations in six of these clusters where we see enhanced [Na/Fe] > +0.25 dex. We obtain the first abundance measurements of Cr, Mn, and Ni for a sample of the GC population in NGC 5128 and find consistency with the overall trends observed in the MW, with a slight enhancement (<0.1 dex) in the Fe-peak abundances measured in the NGC 5128.

Chemical Abundances of Two Stars in the Large Magellanic Cloud Globular Cluster NGC 1718

NASA Astrophysics Data System (ADS)

Sakari, Charli M.; McWilliam, Andrew; Wallerstein, George

2017-05-01

Detailed chemical abundances of two stars in the intermediate-age Large Magellanic Cloud (LMC) globular cluster NGC 1718 are presented, based on high-resolution spectroscopic observations with the MIKE spectrograph. The detailed abundances confirm NGC 1718 to be a fairly metal-rich cluster, with an average [Fe/H] ˜ -0.55 ± 0.01. The two red giants appear to have primordial O, Na, Mg and Al abundances, with no convincing signs of a composition difference between the two stars - hence, based on these two stars, NGC 1718 shows no evidence for hosting multiple populations. The Mg abundance is lower than Milky Way field stars, but is similar to LMC field stars at the same metallicity. The previous claims of very low [Mg/Fe] in NGC 1718 are therefore not supported in this study. Other abundances (Si, Ca, Ti, V, Mn, Ni, Cu, Rb, Y, Zr, La and Eu) all follow the LMC field star trend, demonstrating yet again that (for most elements) globular clusters trace the abundances of their host galaxy's field stars. Similar to the field stars, NGC 1718 is found to be mildly deficient in explosive α-elements, but moderately to strongly deficient in O, Na, Mg, Al and Cu, elements that form during hydrostatic burning in massive stars. NGC 1718 is also enhanced in La, suggesting that it was enriched in ejecta from metal-poor asymptotic giant branch stars.

Water cluster fragmentation probed by pickup experiments

NASA Astrophysics Data System (ADS)

Huang, Chuanfu; Kresin, Vitaly V.; Pysanenko, Andriy; Fárník, Michal

2016-09-01

Electron ionization is a common tool for the mass spectrometry of atomic and molecular clusters. Any cluster can be ionized efficiently by sufficiently energetic electrons, but concomitant fragmentation can seriously obstruct the goal of size-resolved detection. We present a new general method to assess the original neutral population of the cluster beam. Clusters undergo a sticking collision with a molecule from a crossed beam, and the velocities of neat and doped cluster ion peaks are measured and compared. By making use of longitudinal momentum conservation, one can reconstruct the sizes of the neutral precursors. Here this method is applied to H2O and D2O clusters in the detected ion size range of 3-10. It is found that water clusters do fragment significantly upon electron impact: the deduced neutral precursor size is ˜3-5 times larger than the observed cluster ions. This conclusion agrees with beam size characterization by another experimental technique: photoionization after Na-doping. Abundant post-ionization fragmentation of water clusters must therefore be an important factor in the interpretation of experimental data; interestingly, there is at present no detailed microscopic understanding of the underlying fragmentation dynamics.

Stability and minimum size of colloidal clusters on a liquid-air interface.

PubMed

Pergamenshchik, V M

2012-02-01

A vertical force applied to each of two colloids, trapped at a liquid-air interface, induces their logarithmic pairwise attraction. I recently showed [Phys. Rev. E 79, 011407 (2009)] that in clusters of size R much larger than the capillary length λ, the attraction changes to that of a power law and is much stronger due to a many-body effect, and I derived two equations that describe the equilibrium coarse-grained meniscus profile and colloid density in such clusters. In this paper, this theory is shown also to describe small clusters with R≪ λ provided the number N of colloids therein is sufficiently large. An analytical solution for a small circular cluster with an arbitrary short-range power-law pairwise repulsion is found. The energy of a cluster is obtained as a function of its radius R and colloid number N. As in large clusters, the attraction force and energy universally scale with the distance L between colloids as L(-3) and L(-2), respectively, for any repulsion forces. The states of an equilibrium cluster, predicted by the theory, are shown to be stable with respect to small perturbations of the meniscus profile and colloid density. The minimum number of colloids in a circular cluster, which sustains the thermal motion, is estimated. For standard parameters, it can be very modest, e.g., in the range 20-200, which is in line with experimental findings on reversible clusterization on a liquid-air interface. © 2012 American Physical Society

Evaluation of Spin Hamiltonian Parameters and Local Structure of Cu2+-doped Ion in xK2SO4-(50 - x)Na2SO4-50ZnSO4 Glasses with Various K2SO4 Concentrations

NASA Astrophysics Data System (ADS)

Ding, Ch.-Ch.; Wu, Sh.-Y.; Xu, Y.-Q.; Zhang, L.-J.; He, J.-J.

2018-03-01

The spin Hamiltonian parameters (SHPs), i.e., g factors and hyperfine structure constants, and local structures are theoretically studied by analyzing tetragonally elongated 3d9 clusters for Cu2+ in xK2SO4-(50 - x)Na2SO4-50ZnSO4 glasses with various K2SO4 concentrations x. The concentration dependences of the SHPs are attributed to the parabolic decreases of the cubic field parameter Dq, orbital reduction factor k, relative tetragonal elongation ratio τ, and core polarization constant κ with x. The [CuO6]10- clusters are found to undergo significant elongations of about 17% due to the Jahn-Teller effect. The calculated cubic field splittings and the SHPs at various concentrations agree well with the experimental data.

Small traveling clusters in attractive and repulsive Hamiltonian mean-field models.

PubMed

Barré, Julien; Yamaguchi, Yoshiyuki Y

2009-03-01

Long-lasting small traveling clusters are studied in the Hamiltonian mean-field model by comparing between attractive and repulsive interactions. Nonlinear Landau damping theory predicts that a Gaussian momentum distribution on a spatially homogeneous background permits the existence of traveling clusters in the repulsive case, as in plasma systems, but not in the attractive case. Nevertheless, extending the analysis to a two-parameter family of momentum distributions of Fermi-Dirac type, we theoretically predict the existence of traveling clusters in the attractive case; these findings are confirmed by direct N -body numerical simulations. The parameter region with the traveling clusters is much reduced in the attractive case with respect to the repulsive case.

Clustering of water molecules in ultramicroporous carbon: In-situ small-angle neutron scattering

DOE PAGES

Bahadur, Jitendra; Contescu, Cristian I.; Rai, Durgesh K.; ...

2016-10-19

The adsorption of water is central to most of the applications of microporous carbon as adsorbent material. We report early kinetics of water adsorption in the microporous carbon using in-situ small-angle neutron scattering. It is observed that adsorption of water occurs via cluster formation of molecules. Interestingly, the cluster size remains constant throughout the adsorption process whereas number density of clusters increases with time. The role of surface chemistry of microporous carbon on the early kinetics of adsorption process was also investigated. Lastly, the present study provides direct experimental evidence for cluster assisted adsorption of water molecules in microporous carbonmore » (Do-Do model).« less

Multivariate statistical techniques for the evaluation of groundwater quality of Amaravathi River Basin: South India

NASA Astrophysics Data System (ADS)

Loganathan, K.; Ahamed, A. Jafar

2017-12-01

The study of groundwater in Amaravathi River basin of Karur District resulted in large geochemical data set. A total of 24 water samples were collected and analyzed for physico-chemical parameters, and the abundance of cation and anion concentrations was in the following order: Na+ > Ca2+ > Mg2+ > K+ = Cl- > HCO3 - > SO4 2-. Correlation matrix shows that the basic ionic chemistry is influenced by Na+, Ca2+, Mg2+, and Cl-, and also suggests that the samples contain Na+-Cl-, Ca2+-Cl- an,d mixed Ca2+-Mg2+-Cl- types of water. HCO3 -, SO4 2-, and F- association is less than that of other parameters due to poor or less available of bearing minerals. PCA extracted six components, which are accountable for the data composition explaining 81% of the total variance of the data set and allowed to set the selected parameters according to regular features as well as to evaluate the frequency of each group on the overall variation in water quality. Cluster analysis results show that groundwater quality does not vary extensively as a function of seasons, but shows two main clusters.

Theoretical and experimental insights into the origin of the catalytic activity of subnanometric gold clusters: attempts to predict reactivity with clusters and nanoparticles of gold.

PubMed

Boronat, Mercedes; Leyva-Pérez, Antonio; Corma, Avelino

2014-03-18

Particle size is one of the key parameters determining the unexpected catalytic activity of gold, with reactivity improving as the particle gets smaller. While this is valid in the 1-5 nm range, chemists are now investigating the influence of particle size in the subnanometer regime. This is due to recent advances in both characterization techniques and synthetic routes capable of stabilizing these size-controlled gold clusters. Researchers reported in early studies that small clusters or aggregates of a few atoms can be extremely active in some reactions, while 1-2 nm nanoparticles are catalytically more efficient for other reactions. Furthermore, the possibility that small gold clusters generated in situ from gold salts or complexes could be the real active species in homogeneous gold-catalyzed organic reactions should be considered. In this Account, we address two questions. First, what is the origin of the enhanced reactivity of gold clusters on the subnanometer scale? And second, how can we predict the reactions where small clusters should work better than larger nanoparticles? Both geometric factors and electronic or quantum size effects become important in the subnanometer regime. Geometric reasons play a key role in hydrogenation reactions, where only accessible low coordinated neutral Au atoms are needed to dissociate H2. The quantum size effects of gold clusters are important as well, as clusters formed by only a few atoms have discrete molecule-like electronic states and their chemical reactivity is related to interactions between the cluster's frontier molecular orbitals and those of the reactant molecules. From first principles calculations, we predict an enhanced reactivity of small planar clusters for reactions involving activation of CC multiple bonds in alkenes and alkynes through Lewis acid-base interactions, and a better catalytic performance of 3D gold nanoparticles in redox reactions involving bond dissociation by oxidative addition and new bond formation by reductive elimination. In oxidation reactions with molecular O2, initial dissociation of O2 into basic oxygen atoms would be more effectively catalyzed by gold nanoparticles of ∼1 nm diameter. In contrast, small planar clusters should be more active for reactions following a radical pathway involving peroxo or hydroperoxo intermediates. We have experimentally confirmed these predictions for a series of Lewis acid and oxidation reactions catalyzed by gold clusters and nanoparticles either in solution or supported on solid carriers.

Globular Cluster Abundances from High-Resolution Integrated-Light Spectra. I. 47 Tuc

NASA Astrophysics Data System (ADS)

McWilliam, Andrew; Bernstein, Rebecca A.

2008-09-01

We describe the detailed chemical abundance analysis of a high-resolution (R ~ 35,000), integrated-light (IL), spectrum of the core of the Galactic globular cluster 47 Tuc, obtained using the du Pont echelle at Las Campanas. We develop an abundance analysis strategy that can be applied to spatial unresolved extragalactic clusters. We have computed abundances for Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Ba, La, Nd, and Eu. For an analysis with the known color-magnitude diagram (CMD) for 47 Tuc we obtain a mean [Fe/H] value of -0.75 +/- 0.026 +/- 0.045 dex (random and systematic error), in good agreement with the mean of five recent high-resolution abundance studies, at -0.70 dex. Typical random errors on our mean [X/Fe] ratios are 0.07-0.10 dex, similar to studies of individual stars in 47 Tuc. Na and Al appear enhanced, perhaps due to proton burning in the most luminous cluster stars. Our IL abundance analysis with an unknown CMD employed theoretical Teramo isochrones; however, we apply zero-point abundance corrections to account for the factor of 3 underprediction of stars at the AGB bump luminosity. While line diagnostics alone provide only mild constraints on the cluster age (ruling out ages younger than ~2 Gyr), when theoretical IL B - V colors are combined with metallicity derived from the Fe I lines, the age is constrained to 10-15 Gyr and we obtain [ Fe/H ] = - 0.70 +/- 0.021 +/- 0.052 dex. We find that Fe I line diagnostics may also be used to constrain the horizontal-branch morphology of an unresolved cluster. Lastly, our spectrum synthesis of 5.4 million TiO lines indicates that the 7300-7600 Å TiO window should be useful for estimating the effect of M giants on the IL abundances, and important for clusters more metal-rich than 47 Tuc.

Cluster Free Energies from Simple Simulations of Small Numbers of Aggregants: Nucleation of Liquid MTBE from Vapor and Aqueous Phases.

PubMed

Patel, Lara A; Kindt, James T

2017-03-14

We introduce a global fitting analysis method to obtain free energies of association of noncovalent molecular clusters using equilibrated cluster size distributions from unbiased constant-temperature molecular dynamics (MD) simulations. Because the systems simulated are small enough that the law of mass action does not describe the aggregation statistics, the method relies on iteratively determining a set of cluster free energies that, using appropriately weighted sums over all possible partitions of N monomers into clusters, produces the best-fit size distribution. The quality of these fits can be used as an objective measure of self-consistency to optimize the cutoff distance that determines how clusters are defined. To showcase the method, we have simulated a united-atom model of methyl tert-butyl ether (MTBE) in the vapor phase and in explicit water solution over a range of system sizes (up to 95 MTBE in the vapor phase and 60 MTBE in the aqueous phase) and concentrations at 273 K. The resulting size-dependent cluster free energy functions follow a form derived from classical nucleation theory (CNT) quite well over the full range of cluster sizes, although deviations are more pronounced for small cluster sizes. The CNT fit to cluster free energies yielded surface tensions that were in both cases lower than those for the simulated planar interfaces. We use a simple model to derive a condition for minimizing non-ideal effects on cluster size distributions and show that the cutoff distance that yields the best global fit is consistent with this condition.

The peculiar Na-O anticorrelation of the bulge globular cluster NGC 6440

NASA Astrophysics Data System (ADS)

Muñoz, C.; Villanova, S.; Geisler, D.; Saviane, I.; Dias, B.; Cohen, R. E.; Mauro, F.

2017-08-01

Context. Galactic globular clusters (GCs) are essential tools for understanding the earliest epoch of the Milky Way, since they are among the oldest objects in the Universe and can be used to trace its formation and evolution. Current studies using high-resolution spectroscopy for many stars in each of a large sample of GCs allow us to develop a detailed observational picture of their formation and their relation with the Galaxy. However, it is necessary to complete this picture by including GCs that belong to all major Galactic components, including the bulge. Aims: Our aim is to perform a detailed chemical analysis of the bulge GC NGC 6440 in order to determine if this object has multiple populations (MPs) and investigate its relation with the bulge of the Milky Way and with the other Galactic GCs, especially those associated with the bulge, which are largely poorly studied. Methods: We determined the stellar parameters and the chemical abundances of light elements (Na, Al), iron-peak elements (Fe, Sc, Mn, Co, Ni), α-elements (O, Mg, Si, Ca, Ti) and heavy elements (Ba, Eu) in seven red giant members of NGC 6440 using high-resolution spectroscopy from FLAMES-UVES. Results: We found a mean iron content of [Fe/H] =-0.50 ± 0.03 dex in agreement with other studies. We found no internal iron spread. On the other hand, Na and Al show a significant intrinsic spread, but the cluster has no significant O-Na anticorrelation nor does it exhibit a Mg-Al anticorrelation. The α-elements show good agreement with the bulge field star trend, although they are at the high alpha end and are also higher than those of other GCs of comparable metallicity. The heavy elements are dominated by the r-process, indicating a strong contribution by SNeII. The chemical analysis suggests an origin similar to that of the bulge field stars.

Self-Assembled Upconversion Nanoparticle Clusters for NIR-controlled Drug Release and Synergistic Therapy after Conjugation with Gold Nanoparticles.

PubMed

Cai, Huijuan; Shen, Tingting; Kirillov, Alexander M; Zhang, Yu; Shan, Changfu; Li, Xiang; Liu, Weisheng; Tang, Yu

2017-05-01

Fabricated three-dimensional (3D) upconversion nanoclusters (abbreviated as EBSUCNPs) are obtained via an emulsion-based bottom-up self-assembly of NaGdF 4 :Yb/Er@NaGdF 4 nanoparticles (abbreviated as UCNPs), which comprise a NaGdF 4 :Yb/Er core and a NaGdF 4 shell. The EBSUCNPs were then coated with a thin mesoporous amino-functionalized SiO 2 shell (resulting in EBSUCNPs@SiO 2 precursor) and further conjugated with gold nanoparticles to give the novel EBSUCNPs@SiO 2 @Au material. Finally, EBSUCNPs@SiO 2 @Au was applied as a biocompatible and efficient drug carrier for doxorubicin (DOX), thus giving rise to a multifunctional EBSUCNPs@SiO 2 -DOX@Au nanocomposite. This final material, EBSUCNPs@SiO 2 -DOX@Au, and the precursor nanoparticles, EBSUCNPs@SiO 2 @Au, were both fully characterized and their luminescence was investigated in detail. In addition, the drug release properties and photothermal effects of EBSUCNPs@SiO 2 -DOX@Au were also discussed. Interestingly, when under NIR irradiation, an increasing DOX release was achieved owing to the thermal effect of the Au NPs after absorbing the green light from the upconversion nanoclusters based on the fluorescence resonance energy transfer (FRET) effect. Thus, a near-infrared (NIR)-controlled "on-off" pattern of drug release behavior can be achieved. Moreover, compared with a single therapy method, the assembled nanocomposites exhibit a good synergistic therapy against cancer cells that combines chemotherapy with photothermal therapy. In addition, the in vitro fluorescence microscopy images of EBSUCNPs@SiO 2 -DOX@Au show a higher enhancement in the red region due to the loading of DOX molecules with respect to EBSUCNPs@SiO 2 @Au. Therefore, this novel multifunctional 3D cluster architecture can be used in the biomedical field after modification and may pave a new way in other application areas of UCNPs clusters.

Delivery of Iron-Sulfur Clusters to the Hydrogen-Oxidizing [NiFe]-Hydrogenases in Escherichia coli Requires the A-Type Carrier Proteins ErpA and IscA

PubMed Central

Pinske, Constanze; Sawers, R. Gary

2012-01-01

During anaerobic growth Escherichia coli synthesizes two membrane-associated hydrogen-oxidizing [NiFe]-hydrogenases, termed hydrogenase 1 and hydrogenase 2. Each enzyme comprises a catalytic subunit containing the [NiFe] cofactor, an electron-transferring small subunit with a particular complement of [Fe-S] (iron-sulfur) clusters and a membrane-anchor subunit. How the [Fe-S] clusters are delivered to the small subunit of these enzymes is unclear. A-type carrier (ATC) proteins of the Isc (iron-sulfur-cluster) and Suf (sulfur mobilization) [Fe-S] cluster biogenesis pathways are proposed to traffic pre-formed [Fe-S] clusters to apoprotein targets. Mutants that could not synthesize SufA had active hydrogenase 1 and hydrogenase 2 enzymes, thus demonstrating that the Suf machinery is not required for hydrogenase maturation. In contrast, mutants devoid of the IscA, ErpA or IscU proteins of the Isc machinery had no detectable hydrogenase 1 or 2 activities. Lack of activity of both enzymes correlated with the absence of the respective [Fe-S]-cluster-containing small subunit, which was apparently rapidly degraded. During biosynthesis the hydrogenase large subunits receive their [NiFe] cofactor from the Hyp maturation machinery. Subsequent to cofactor insertion a specific C-terminal processing step occurs before association of the large subunit with the small subunit. This processing step is independent of small subunit maturation. Using western blotting experiments it could be shown that although the amount of each hydrogenase large subunit was strongly reduced in the iscA and erpA mutants, some maturation of the large subunit still occurred. Moreover, in contrast to the situation in Isc-proficient strains, these processed large subunits were not membrane-associated. Taken together, our findings demonstrate that both IscA and ErpA are required for [Fe-S] cluster delivery to the small subunits of the hydrogen-oxidizing hydrogenases; however, delivery of the Fe atom to the active site might have different requirements. PMID:22363723

βIV Spectrinopathies Cause Profound Intellectual Disability, Congenital Hypotonia, and Motor Axonal Neuropathy.

PubMed

Wang, Chih-Chuan; Ortiz-González, Xilma R; Yum, Sabrina W; Gill, Sara M; White, Amy; Kelter, Erin; Seaver, Laurie H; Lee, Sansan; Wiley, Graham; Gaffney, Patrick M; Wierenga, Klaas J; Rasband, Matthew N

2018-06-07

βIV spectrin links ankyrinG (AnkG) and clustered ion channels at axon initial segments (AISs) and nodes of Ranvier to the axonal cytoskeleton. Here, we report bi-allelic pathogenic SPTBN4 variants (three homozygous and two compound heterozygous) that cause a severe neurological syndrome that includes congenital hypotonia, intellectual disability, and motor axonal and auditory neuropathy. We introduced these variants into βIV spectrin, expressed these in neurons, and found that 5/7 were loss-of-function variants disrupting AIS localization or abolishing phosphoinositide binding. Nerve biopsies from an individual with a loss-of-function variant had reduced nodal Na + channels and no nodal KCNQ2 K + channels. Modeling the disease in mice revealed that although ankyrinR (AnkR) and βI spectrin can cluster Na + channels and partially compensate for the loss of AnkG and βIV spectrin at nodes of Ranvier, AnkR and βI spectrin cannot cluster KCNQ2- and KCNQ3-subunit-containing K + channels. Our findings define a class of spectrinopathies and reveal the molecular pathologies causing nervous-system dysfunction. Copyright © 2018 American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.

Magnetic nanostructures.

PubMed

Bennemann, K

2010-06-23

Characteristic results of magnetism in small particles, thin films and tunnel junctions are presented. As a consequence of the reduced atomic coordination in small clusters and thin films the electronic states and density of states are modified. Thus, magnetic moments and magnetization are affected. Generally, in clusters and thin films magnetic anisotropy plays a special role. In tunnel junctions the interplay of magnetism, spin currents and superconductivity are of particular interest. In ring-like mesoscopic systems Aharonov-Bohm-induced currents are studied. Results are given for single transition metal clusters, cluster ensembles, thin films, mesoscopic structures and tunnel systems. © 2010 IOP Publishing Ltd

Analysis of radiation-induced small Cu particle cluster formation in aqueous CuCl2

USGS Publications Warehouse

Jayanetti, Sumedha; Mayanovic, Robert A.; Anderson, Alan J.; Bassett, William A.; Chou, I.-Ming

2001-01-01

Radition-induced small Cu particle cluster formation in aqueous CuCl2 was analyzed. It was noticed that nearest neighbor distance increased with the increase in the time of irradiation. This showed that the clusters approached the lattice dimension of bulk copper. As the average cluster size approached its bulk dimensions, an increase in the nearest neighbor coordination number was found with the decrease in the surface to volume ratio. Radiolysis of water by incident x-ray beam led to the reduction of copper ions in the solution to themetallic state.

Quantum and Classical Molecular Dynamics of Ionic Liquid Electrolytes for Na/Li-based Batteries: Molecular Origins of the Conductivity Behavior.

PubMed

Vicent-Luna, Jose Manuel; Ortiz-Roldan, Jose Manuel; Hamad, Said; Tena-Zaera, Ramon; Calero, Sofia; Anta, Juan Antonio

2016-08-18

Compositional effects on the charge-transport properties of electrolytes for batteries based on room-temperature ionic liquids (RTILs) are well-known. However, further understanding is required about the molecular origins of these effects, in particular regarding the replacement of Li by Na. In this work, we investigate the use of RTILs in batteries, by means of both classical molecular dynamics (MD), which provides information about structure and molecular transport, and ab initio molecular dynamics (AIMD), which provides information about structure. The focus has been placed on the effect of adding either Na(+) or Li(+) to 1-methyl-1-butyl-pyrrolidinium [C4 PYR](+) bis(trifluoromethanesulfonyl)imide [Tf2 N](-) . Radial distribution functions show excellent agreement between MD and AIMD, which ensures the validity of the force fields used in the MD. This is corroborated by the MD results for the density, the diffusion coefficients, and the total conductivity of the electrolytes, which reproduce remarkably well the experimental observations for all studied Na/Li concentrations. By extracting partial conductivities, it is demonstrated that the main contribution to the conductivity is that of [C4 PYR](+) and [Tf2 N](-) . However, addition of Na(+) /Li(+) , although not significant on its own, produces a dramatic decrease in the partial conductivities of the RTIL ions. The origin of this indirect effect can be traced to the modification of the microscopic structure of the liquid as observed from the radial distribution functions, owing to the formation of [Na(Tf2 N)n ]((n-1)-) and [Li(Tf2 N)n ]((n-1)-) clusters at high concentrations. This formation hinders the motion of the large ions, hence reducing the total conductivity. We demonstrate that this clustering effect is common to both Li and Na, showing that both ions behave in a similar manner at a microscopic level in spite of their distinct ionic radii. This is an interesting finding for extending Li-ion and Li-air technologies to their potentially cheaper Na-based counterparts. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Monogenetic Volcano Clusters within the wider Michoacán-Guanajuato Volcanic Field (México) and their Significance

NASA Astrophysics Data System (ADS)

Siebe, C.

2017-12-01

The Trans-Mexican Volcanic Belt, one of the most complex and active continental arcs worldwide, displays several volcanic fields dominated by monogenetic volcanoes. Of these, the Plio-Quaternary Michoacán-Guanajuato Volcanic Field (MGVF) situated in central Mexico, is the largest monogenetic volcanic field in the world and includes more than 1000 scoria cones and associated lava flows and about 400 medium-sized volcanoes (Mexican shields). The smaller monogenetic vents occur either isolated or form small clusters within the wider MGVF. The recent identification of small clusters comprising several monogenetic volcanoes that erupted in a sequence of geologically short time intervals (hundreds to few thousands of years) in small areas within the much wider MGVF opens several questions in regard to future volcanic hazard assessments in this region: Are the youngest (Holocene) clusters still "active" and is a new eruption likely to occur within their surroundings? How long are such clusters "active"? Will the next monogenetic eruption in the MGVF be a single short-lived isolated eruption, or the beginning of a cluster? Furthermore, is it possible that the historic eruptions of Jorullo (1759) and Paricutin (1943) represent each the beginning of a cluster and should a new eruption in their proximity be expected in the future? In order to address these questions, two Holocene clusters, namely Tacámbaro and Malpaís de Zacapu are currently under study and preliminary results will be presented. Each comprises four monogenetic vents that erupted in a sequence of geologically short time intervals (hundreds to few thousands of years) within a small area (few tens of km2) Geologic mapping, geochemical analyses, radiometric dating, and paleomagnetic studies will help to establish the sequence of eruption of the different vents, and shed more light on the conditions that allow several magma sources to be formed and then tapped in close temporal and spatial proximity to each other and produce such small "flare-ups".

Cluster size dependence of high-order harmonic generation

NASA Astrophysics Data System (ADS)

Tao, Y.; Hagmeijer, R.; Bastiaens, H. M. J.; Goh, S. J.; van der Slot, P. J. M.; Biedron, S. G.; Milton, S. V.; Boller, K.-J.

2017-08-01

We investigate high-order harmonic generation (HHG) from noble gas clusters in a supersonic gas jet. To identify the contribution of harmonic generation from clusters versus that from gas monomers, we measure the high-order harmonic output over a broad range of the total atomic number density in the jet (from 3×1016 to 3 × 1018 {{cm}}-3) at two different reservoir temperatures (303 and 363 K). For the first time in the evaluation of the harmonic yield in such measurements, the variation of the liquid mass fraction, g, versus pressure and temperature is taken into consideration, which we determine, reliably and consistently, to be below 20% within our range of experimental parameters. By comparing the measured harmonic yield from a thin jet with the calculated corresponding yield from monomers alone, we find an increased emission of the harmonics when the average cluster size is less than 3000. Using g, under the assumption that the emission from monomers and clusters add up coherently, we calculate the ratio of the average single-atom response of an atom within a cluster to that of a monomer and find an enhancement of around 100 for very small average cluster size (∼200). We do not find any dependence of the cut-off frequency on the composition of the cluster jet. This implies that HHG in clusters is based on electrons that return to their parent ions and not to neighboring ions in the cluster. To fully employ the enhanced average single-atom response found for small average cluster sizes (∼200), the nozzle producing the cluster jet must provide a large liquid mass fraction at these small cluster sizes for increasing the harmonic yield. Moreover, cluster jets may allow for quasi-phase matching, as the higher mass of clusters allows for a higher density contrast in spatially structuring the nonlinear medium.

Tantalum induced butterfly-like clusters on Si (111)-7 × 7 surface: STM/STS study at low coverage

NASA Astrophysics Data System (ADS)

Shukrynau, Pavel; Mutombo, Pingo; Švec, Martin; Hietschold, Michael; Cháb, Vladimír

2012-02-01

The adsorption of the small amounts of tantalum on Si (111)-7 × 7 reconstructed surface is investigated systematically using scanning tunneling microscopy and tunneling spectroscopy combined with first-principles density functional theory calculations. We find out that the moderate annealing of the Ta covered surface results in the formation of clusters of the butterfly-like shape. The clusters are sporadically distributed over the surface and their density is metal coverage dependent. Filled and empty state STM images of the clusters differ strongly suggesting the existence of covalent bonds within the cluster. Tunneling spectroscopy measurements reveal small energy gap, showing semiconductor-like behavior of the constituent atoms. The cluster model based on experimental images and theoretical calculations has been proposed and discussed. Presented results show that Ta joins the family of adsorbates, that are known to form magic clusters on Si (111)-7 × 7, but its magic cluster has the structural and electronic properties that are different from those reported before.

The SUNBIRD survey: characterizing the super star cluster populations of intensely star-forming galaxies

NASA Astrophysics Data System (ADS)

Randriamanakoto, Zara; Väisänen, Petri

2017-03-01

Super star clusters (SSCs) represent the youngest and most massive form of known gravitationally bound star clusters in the Universe. They are born abundantly in environments that trigger strong and violent star formation. We investigate the properties of these massive SSCs in a sample of 42 nearby starbursts and luminous infrared galaxies. The targets form the sample of the SUperNovae and starBursts in the InfraReD (SUNBIRD) survey that were imaged using near-infrared (NIR) K-band adaptive optics mounted on the Gemini/NIRI and the VLT/NaCo instruments. Results from i) the fitted power-laws to the SSC K-band luminosity functions, ii) the NIR brightest star cluster magnitude - star formation rate (SFR) relation and iii) the star cluster age and mass distributions have shown the importance of studying SSC host galaxies with high SFR levels to determine the role of the galactic environments in the star cluster formation, evolution and disruption mechanisms.

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

NASA Astrophysics Data System (ADS)

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

1997-08-01

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

Pair natural orbital and canonical coupled cluster reaction enthalpies involving light to heavy alkali and alkaline earth metals: the importance of sub-valence correlation.

PubMed

Minenkov, Yury; Bistoni, Giovanni; Riplinger, Christoph; Auer, Alexander A; Neese, Frank; Cavallo, Luigi

2017-04-05

In this work, we tested canonical and domain based pair natural orbital coupled cluster methods (CCSD(T) and DLPNO-CCSD(T), respectively) for a set of 32 ligand exchange and association/dissociation reaction enthalpies involving ionic complexes of Li, Be, Na, Mg, Ca, Sr, Ba and Pb(ii). Two strategies were investigated: in the former, only valence electrons were included in the correlation treatment, giving rise to the computationally very efficient FC (frozen core) approach; in the latter, all non-ECP electrons were included in the correlation treatment, giving rise to the AE (all electron) approach. Apart from reactions involving Li and Be, the FC approach resulted in non-homogeneous performance. The FC approach leads to very small errors (<2 kcal mol -1 ) for some reactions of Na, Mg, Ca, Sr, Ba and Pb, while for a few reactions of Ca and Ba deviations up to 40 kcal mol -1 have been obtained. Large errors are both due to artificial mixing of the core (sub-valence) orbitals of metals and the valence orbitals of oxygen and halogens in the molecular orbitals treated as core, and due to neglecting core-core and core-valence correlation effects. These large errors are reduced to a few kcal mol -1 if the AE approach is used or the sub-valence orbitals of metals are included in the correlation treatment. On the technical side, the CCSD(T) and DLPNO-CCSD(T) results differ by a fraction of kcal mol -1 , indicating the latter method as the perfect choice when the CPU efficiency is essential. For completely black-box applications, as requested in catalysis or thermochemical calculations, we recommend the DLPNO-CCSD(T) method with all electrons that are not covered by effective core potentials included in the correlation treatment and correlation-consistent polarized core valence basis sets of cc-pwCVQZ(-PP) quality.

Local Higher-Order Graph Clustering

PubMed Central

Yin, Hao; Benson, Austin R.; Leskovec, Jure; Gleich, David F.

2018-01-01

Local graph clustering methods aim to find a cluster of nodes by exploring a small region of the graph. These methods are attractive because they enable targeted clustering around a given seed node and are faster than traditional global graph clustering methods because their runtime does not depend on the size of the input graph. However, current local graph partitioning methods are not designed to account for the higher-order structures crucial to the network, nor can they effectively handle directed networks. Here we introduce a new class of local graph clustering methods that address these issues by incorporating higher-order network information captured by small subgraphs, also called network motifs. We develop the Motif-based Approximate Personalized PageRank (MAPPR) algorithm that finds clusters containing a seed node with minimal motif conductance, a generalization of the conductance metric for network motifs. We generalize existing theory to prove the fast running time (independent of the size of the graph) and obtain theoretical guarantees on the cluster quality (in terms of motif conductance). We also develop a theory of node neighborhoods for finding sets that have small motif conductance, and apply these results to the case of finding good seed nodes to use as input to the MAPPR algorithm. Experimental validation on community detection tasks in both synthetic and real-world networks, shows that our new framework MAPPR outperforms the current edge-based personalized PageRank methodology. PMID:29770258

Sugar-influenced water diffusion, interaction, and retention in clay interlayer nanopores probed by theoretical simulations and experimental spectroscopies

NASA Astrophysics Data System (ADS)

Aristilde, Ludmilla; Galdi, Stephen M.; Kelch, Sabrina E.; Aoki, Thalia G.

2017-08-01

Understanding the hydrodynamics in clay nanopores is important for gaining insights into the trapping of water, nutrients, and contaminants in natural and engineered soils. Previous investigations have focused on the interlayer organization and molecular diffusion coefficients (D) of cations and water molecules in cation-saturated interlayer nanopores of smectite clays. Little is known, however, about how these interlayer dynamic properties are influenced by the ubiquitous presence of small organic compounds such as sugars in the soil environment. Here we probed the effects of glucose molecules on montmorillonite interlayer properties. Molecular dynamics simulations revealed re-structuring of the interlayer organization of the adsorptive species. Water-water interactions were disrupted by glucose-water H-bonding interactions. ;Dehydration; of the glucose-populated nanopore led to depletion in the Na solvation shell, which resulted in the accumulation of both Na ions (as inner-sphere complexes) and remaining hydrated water molecules at the mineral surface. This accumulation led to a decrease in both DNa and Dwater. In addition, the reduction in Dglucose as a function of increasing glucose content can be explained by the aggregation of glucose molecules into organic clusters H-bonded to the mineral surface on both walls of the nanopore. Experimental nuclear magnetic resonance and X-ray diffraction data were consistent with the theoretical predictions. Compared to clay interlayers devoid of glucose, increased intensities and new peaks in the 23Na nuclear magnetic resonance spectra confirmed increasing immobilization of Na as a function of increasing glucose content. And, the X-ray diffraction data indicated a reduced collapse of glucose-populated interlayers exposed to decreasing moisture conditions, which led to the maintenance of hydrated clay nanopores. The coupling of theoretical and experimental findings sheds light on the molecular to nanoscale mechanisms that control the enhanced trapping of water molecules and solutes within sugar-enriched clay nanopores.

NaK Plugging Meter Design for the Feasibility Test Loops

NASA Technical Reports Server (NTRS)

Pearson, J. Boise; Godfroy, Thomas J.; Reid, Robert S.; Polzin, Kurt A.

2008-01-01

The design and predicted performance of a plugging meter for use in the measurement of NaK impurity levels are presented. The plugging meter is incorporated into a Feasibility Test Loop (FTL), which is a small pumped-NaK loop designed to enable the rapid, small-scale evaluation of techniques such as in situ purification methods and to permit the measurement of bulk material transport effects (not mechanisms) under flow conditions that are representative of a fission surface power reactor. The FTL operates at temperatures similar to those found in a reactor, with a maximum hot side temperature of 900 K and a corresponding cold side temperature of 860 K. In the plugging meter a low flow rate bypass loop is cooled until various impurities (primarily oxides) precipitate out of solution. The temperatures at which these impurities precipitate are indicative of the level of impurities in the NaK. The precipitates incrementally plug a small orifice in the bypass loop, which is detected by monitoring changes in the liquid metal flow rate.

Potential energy curves of the Na2+ molecular ion from all-electron ab initio relativistic calculations

NASA Astrophysics Data System (ADS)

Bewicz, Anna; Musiał, Monika; Kucharski, Stanisław A.

2017-11-01

The equation-of-motion coupled-cluster method for electron affinity calculations has been used to study potential energy curves (PECs) for the Na+2 molecular ion. Although the studied molecule represents the open shell system the applied approach employs the closed shell Na+ 22 ion as the reference. In addition the Na+ 22 system dissociates into the closed shell fragments; hence, the restricted Hartree-Fock scheme can be used within the whole range of interatomic distances, from 2 to 45 Å. We used large basis set engaging 268 basis functions with all 21 electrons correlated. The relativistic effects are included via second-order Douglas-Kroll method. The computed PECs, spectroscopic molecular constants and vibrational energy levels agree well with experimental values if the latter are available or with other theoretical data.

Tuberculosis outbreaks predicted by characteristics of first patients in a DNA fingerprint cluster.

PubMed

Kik, Sandra V; Verver, Suzanne; van Soolingen, Dick; de Haas, Petra E W; Cobelens, Frank G; Kremer, Kristin; van Deutekom, Henk; Borgdorff, Martien W

2008-07-01

Some clusters of patients who have Mycobacterium tuberculosis isolates with identical DNA fingerprint patterns grow faster than others. It is unclear what predictors determine cluster growth. To assess whether the development of a tuberculosis (TB) outbreak can be predicted by the characteristics of its first two patients. Demographic and clinical data of all culture-confirmed patients with TB in the Netherlands from 1993 through 2004 were combined with DNA fingerprint data. Clusters were restricted to cluster episodes of 2 years to only detect newly arising clusters. Characteristics of the first two patients were compared between small (2-4 cases) and large (5 or more cases) cluster episodes. Of 5,454 clustered cases, 1,756 (32%) were part of a cluster episode of 2 years. Of 622 cluster episodes, 54 (9%) were large and 568 (91%) were small episodes. Independent predictors for large cluster episodes were as follows: less than 3 months' time between the diagnosis of the first two patients, one or both patients were young (<35 yr), both patients lived in an urban area, and both patients came from sub-Saharan Africa. In the Netherlands, patients in new cluster episodes should be screened for these risk factors. When the risk pattern applies, targeted interventions (e.g., intensified contact investigation) should be considered to prevent further cluster expansion.

Extracting Aggregation Free Energies of Mixed Clusters from Simulations of Small Systems: Application to Ionic Surfactant Micelles.

PubMed

Zhang, X; Patel, L A; Beckwith, O; Schneider, R; Weeden, C J; Kindt, J T

2017-11-14

Micelle cluster distributions from molecular dynamics simulations of a solvent-free coarse-grained model of sodium octyl sulfate (SOS) were analyzed using an improved method to extract equilibrium association constants from small-system simulations containing one or two micelle clusters at equilibrium with free surfactants and counterions. The statistical-thermodynamic and mathematical foundations of this partition-enabled analysis of cluster histograms (PEACH) approach are presented. A dramatic reduction in computational time for analysis was achieved through a strategy similar to the selector variable method to circumvent the need for exhaustive enumeration of the possible partitions of surfactants and counterions into clusters. Using statistics from a set of small-system (up to 60 SOS molecules) simulations as input, equilibrium association constants for micelle clusters were obtained as a function of both number of surfactants and number of associated counterions through a global fitting procedure. The resulting free energies were able to accurately predict micelle size and charge distributions in a large (560 molecule) system. The evolution of micelle size and charge with SOS concentration as predicted by the PEACH-derived free energies and by a phenomenological four-parameter model fit, along with the sensitivity of these predictions to variations in cluster definitions, are analyzed and discussed.

Analysis of the electron density features of small boron clusters and the effects of doping with C, P, Al, Si, and Zn: Magic B7P and B8Si clusters

NASA Astrophysics Data System (ADS)

Saha, P.; Rahane, A. B.; Kumar, V.; Sukumar, N.

2016-05-01

Boron atomic clusters show several interesting and unusual size-dependent features due to the small covalent radius, electron deficiency, and higher coordination number of boron as compared to carbon. These include aromaticity and a diverse array of structures such as quasi-planar, ring or tubular shaped, and fullerene-like. In the present work, we have analyzed features of the computed electron density distributions of small boron clusters having up to 11 boron atoms, and investigated the effect of doping with C, P, Al, Si, and Zn atoms on their structural and physical properties, in order to understand the bonding characteristics and discern trends in bonding and stability. We find that in general there are covalent bonds as well as delocalized charge distribution in these clusters. We associate the strong stability of some of these planar/quasiplanar disc-type clusters with the electronic shell closing with effectively twelve delocalized valence electrons using a disc-shaped jellium model. {{{{B}}}9}-, B10, B7P, and B8Si, in particular, are found to be exceptional with very large gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, and these are suggested to be magic clusters.

Synthesis, characterization and optical properties of an amino-functionalized gold thiolate cluster: Au10(SPh-pNH2)10.

PubMed

Lavenn, Christophe; Albrieux, Florian; Tuel, Alain; Demessence, Aude

2014-03-15

Research interest in ultra small gold thiolate clusters has been rising in recent years for the challenges they offer to bring together properties of nanoscience and well-defined materials from molecular chemistry. Here, a new atomically well-defined Au10 gold nanocluster surrounded by ten 4-aminothiophenolate ligands is reported. Its synthesis followed the similar conditions reported for the elaboration of Au144(SR)60, but because the reactivity of thiophenol ligands is different from alkanethiol derivates, smaller Au10 clusters were formed. Different techniques, such as ESI-MS, elemental analysis, XRD, TGA, XPS and UV-vis-NIR experiments, have been carried out to determine the Au10(SPh-pNH2)10 formula. Photoemission experiment has been done and reveals that the Au10 clusters are weakly luminescent as opposed to the amino-based ultra-small gold clusters. This observation points out that the emission of gold thiolate clusters is highly dependent on both the structure of the gold core and the type of the ligands at the surface. In addition, ultra-small amino-functionalized clusters offer the opportunity for extended work on self-assembling networks or deposition on substrates for nanotechnologies or catalytic applications. Copyright © 2013 Elsevier Inc. All rights reserved.

Finite-sample corrected generalized estimating equation of population average treatment effects in stepped wedge cluster randomized trials.

PubMed

Scott, JoAnna M; deCamp, Allan; Juraska, Michal; Fay, Michael P; Gilbert, Peter B

2017-04-01

Stepped wedge designs are increasingly commonplace and advantageous for cluster randomized trials when it is both unethical to assign placebo, and it is logistically difficult to allocate an intervention simultaneously to many clusters. We study marginal mean models fit with generalized estimating equations for assessing treatment effectiveness in stepped wedge cluster randomized trials. This approach has advantages over the more commonly used mixed models that (1) the population-average parameters have an important interpretation for public health applications and (2) they avoid untestable assumptions on latent variable distributions and avoid parametric assumptions about error distributions, therefore, providing more robust evidence on treatment effects. However, cluster randomized trials typically have a small number of clusters, rendering the standard generalized estimating equation sandwich variance estimator biased and highly variable and hence yielding incorrect inferences. We study the usual asymptotic generalized estimating equation inferences (i.e., using sandwich variance estimators and asymptotic normality) and four small-sample corrections to generalized estimating equation for stepped wedge cluster randomized trials and for parallel cluster randomized trials as a comparison. We show by simulation that the small-sample corrections provide improvement, with one correction appearing to provide at least nominal coverage even with only 10 clusters per group. These results demonstrate the viability of the marginal mean approach for both stepped wedge and parallel cluster randomized trials. We also study the comparative performance of the corrected methods for stepped wedge and parallel designs, and describe how the methods can accommodate interval censoring of individual failure times and incorporate semiparametric efficient estimators.

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

Lupi, Laura; Kastelowitz, Noah; Molinero, Valeria, E-mail: Valeria.Molinero@utah.edu

Carbonaceous surfaces are a major source of atmospheric particles and could play an important role in the formation of ice. Here we investigate through molecular simulations the stability, metastability, and molecular pathways of deposition of amorphous ice, bilayer ice, and ice I from water vapor on graphitic and atomless Lennard-Jones surfaces as a function of temperature. We find that bilayer ice is the most stable ice polymorph for small cluster sizes, nevertheless it can grow metastable well above its region of thermodynamic stability. In agreement with experiments, the simulations predict that on increasing temperature the outcome of water deposition ismore » amorphous ice, bilayer ice, ice I, and liquid water. The deposition nucleation of bilayer ice and ice I is preceded by the formation of small liquid clusters, which have two wetting states: bilayer pancake-like (wetting) at small cluster size and droplet-like (non-wetting) at larger cluster size. The wetting state of liquid clusters determines which ice polymorph is nucleated: bilayer ice nucleates from wetting bilayer liquid clusters and ice I from non-wetting liquid clusters. The maximum temperature for nucleation of bilayer ice on flat surfaces, T{sub B}{sup max} is given by the maximum temperature for which liquid water clusters reach the equilibrium melting line of bilayer ice as wetting bilayer clusters. Increasing water-surface attraction stabilizes the pancake-like wetting state of liquid clusters leading to larger T{sub B}{sup max} for the flat non-hydrogen bonding surfaces of this study. The findings of this study should be of relevance for the understanding of ice formation by deposition mode on carbonaceous atmospheric particles, including soot.« less

Anesthesia for euthanasia influences mRNA expression in healthy mice and after traumatic brain injury.

PubMed

Staib-Lasarzik, Irina; Kriege, Oliver; Timaru-Kast, Ralph; Pieter, Dana; Werner, Christian; Engelhard, Kristin; Thal, Serge C

2014-10-01

Tissue sampling for gene expression analysis is usually performed under general anesthesia. Anesthetics are known to modulate hemodynamics, receptor-mediated signaling cascades, and outcome parameters. The present study determined the influence of anesthetic paradigms typically used for euthanization and tissue sampling on cerebral mRNA expression in mice. Naïve mice and animals with acute traumatic brain injury induced by controlled cortical impact (CCI) were randomized to the following euthanasia protocols (n=10-11/group): no anesthesia (NA), 1 min of 4 vol% isoflurane in room air (ISO), 3 min of a combination of 5 mg/kg midazolam, 0.05 mg/kg fentanyl, and 0.5 mg/kg medetomidine intraperitoneally (COMB), or 3 min of 360 mg/kg chloral hydrate intraperitoneally (CH). mRNA expression of actin-1-related gene (Act1), FBJ murine osteosarcoma viral oncogene homolog B (FosB), tumor necrosis factor alpha (TNFα), heat shock protein beta-1 (HspB1), interleukin (IL)-6, tight junction protein 1 (ZO-1), IL-1ß, cyclophilin A, micro RNA 497 (miR497), and small cajal body-specific RNA 17 were determined by real-time polymerase chain reaction (PCR) in hippocampus samples. In naïve animals, Act1 expression was downregulated in the CH group compared with NA. FosB expression was downregulated in COMB and CH groups compared with NA. CCI reduced Act1 and FosB expression, whereas HspB1 and TNFα expression increased. After CCI, HspB1 expression was significantly higher in ISO, COMB, and CH groups, and TNFα expression was elevated in ISO and COMB groups. MiR497, IL-6, and IL-1ß were upregulated after CCI but not affected by anesthetics. Effects were independent of absolute mRNA copy numbers. The data demonstrate that a few minutes of anesthesia before tissue sampling are sufficient to induce immediate mRNA changes, which seem to predominate in the early-regulated gene cluster. Anesthesia-related effects on gene expression might explain limited reproduciblity of real-time PCR data between studies or research groups and should therefore be considered for quantitative PCR data.

Ectoine and 5-hydroxyectoine accumulation in the halophile Virgibacillus halodenitrificans PDB-F2 in response to salt stress.

PubMed

Tao, Ping; Li, Hui; Yu, Yunjiang; Gu, Jidong; Liu, Yongdi

2016-08-01

The moderately halophilic bacterium Virgibacillus halodenitrificans PDB-F2 copes with salinity by synthesizing or taking up compatible solutes. The main compatible solutes in this strain were ectoine and hydroxyectoine, as determined by (1)H nuclear magnetic resonance spectroscopy ((1)H-NMR). A high-performance liquid chromatography (HPLC) analysis showed that ectoine was the major solute that was synthesized in response to elevated salinity, while hydroxyectoine was a minor solute. However, the hydroxyectoine/ectoine ratio increased from 0.04 at 3 % NaCl to 0.45 at 15 % NaCl in the late exponential growth phase. A cluster of ectoine biosynthesis genes was identified, including three genes in the order of ectA, ectB, and ectC. The hydroxyectoine biosynthesis gene ectD was not part of the ectABC gene cluster. Reverse transcription-quantitative polymerase chain reactions (RT-qPCR) showed that the expression of the ect genes was salinity dependent. The expression of ectABC reached a maximum at 12 % NaCl, while ectD expression increased up to 15 % NaCl. Ectoine and hydroxyectoine production was growth phase dependent. The hydroxyectoine/ectoine ratio increased from 0.018 in the early exponential phase to 0.11 in the stationary phase at 5 % NaCl. Hydroxyectoine biosynthesis started much later than ectoine biosynthesis after osmotic shock, and the temporal expression of the ect genes differed under these conditions, with the ectABC genes being expressed first, followed by ectD gene. Increased culture salinity triggered ectoine or hydroxyectoine uptake when they were added to the medium. Hydroxyectoine was accumulated preferentially when both ectoine and hydroxyectoine were provided exogenously.

Nonrandom γ-TuNA-dependent spatial pattern of microtubule nucleation at the Golgi.

PubMed

Sanders, Anna A W M; Chang, Kevin; Zhu, Xiaodong; Thoppil, Roslin J; Holmes, William R; Kaverina, Irina

2017-11-07

Noncentrosomal microtubule (MT) nucleation at the Golgi generates MT network asymmetry in motile vertebrate cells. Investigating the Golgi-derived MT (GDMT) distribution, we find that MT asymmetry arises from nonrandom nucleation sites at the Golgi (hotspots). Using computational simulations, we propose two plausible mechanistic models of GDMT nucleation leading to this phenotype. In the "cooperativity" model, formation of a single GDMT promotes further nucleation at the same site. In the "heterogeneous Golgi" model, MT nucleation is dramatically up-regulated at discrete and sparse locations within the Golgi. While MT clustering in hotspots is equally well described by both models, simulating MT length distributions within the cooperativity model fits the data better. Investigating the molecular mechanism underlying hotspot formation, we have found that hotspots are significantly smaller than a Golgi subdomain positive for scaffolding protein AKAP450, which is thought to recruit GDMT nucleation factors. We have further probed potential roles of known GDMT-promoting molecules, including γ-TuRC-mediated nucleation activator (γ-TuNA) domain-containing proteins and MT stabilizer CLASPs. While both γ-TuNA inhibition and lack of CLASPs resulted in drastically decreased GDMT nucleation, computational modeling revealed that only γ-TuNA inhibition suppressed hotspot formation. We conclude that hotspots require γ-TuNA activity, which facilitates clustered GDMT nucleation at distinct Golgi sites. © 2017 Sanders et al. This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0).

Localization of Ubiquinone-8 in the Na+-pumping NADH:Quinone Oxidoreductase from Vibrio cholerae*

PubMed Central

Casutt, Marco S.; Nedielkov, Ruslan; Wendelspiess, Severin; Vossler, Sara; Gerken, Uwe; Murai, Masatoshi; Miyoshi, Hideto; Möller, Heiko M.; Steuber, Julia

2011-01-01

Na+ is the second major coupling ion at membranes after protons, and many pathogenic bacteria use the sodium-motive force to their advantage. A prominent example is Vibrio cholerae, which relies on the Na+-pumping NADH:quinone oxidoreductase (Na+-NQR) as the first complex in its respiratory chain. The Na+-NQR is a multisubunit, membrane-embedded NADH dehydrogenase that oxidizes NADH and reduces quinone to quinol. Existing models describing redox-driven Na+ translocation by the Na+-NQR are based on the assumption that the pump contains four flavins and one FeS cluster. Here we show that the large, peripheral NqrA subunit of the Na+-NQR binds one molecule of ubiquinone-8. Investigations of the dynamic interaction of NqrA with quinones by surface plasmon resonance and saturation transfer difference NMR reveal a high affinity, which is determined by the methoxy groups at the C-2 and C-3 positions of the quinone headgroup. Using photoactivatable quinone derivatives, it is demonstrated that ubiquinone-8 bound to NqrA occupies a functional site. A novel scheme of electron transfer in Na+-NQR is proposed that is initiated by NADH oxidation on subunit NqrF and leads to quinol formation on subunit NqrA. PMID:21885438

Interactions of small platinum clusters with the TiC(001) surface

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

Mao, Jianjun; Li, Shasha; Chu, Xingli

2015-11-14

Density functional theory calculations are used to elucidate the interactions of small platinum clusters (Pt{sub n}, n = 1–5) with the TiC(001) surface. The results are analyzed in terms of geometric, energetic, and electronic properties. It is found that a single Pt atom prefers to be adsorbed at the C-top site, while a Pt{sub 2} cluster prefers dimerization and a Pt{sub 3} cluster forms a linear structure on the TiC(001). As for the Pt{sub 4} cluster, the three-dimensional distorted tetrahedral structure and the two-dimensional square structure almost have equal stability. In contrast with the two-dimensional isolated Pt{sub 5} cluster, the adsorbed Pt{submore » 5} cluster prefers a three-dimensional structure on TiC(001). Substantial charge transfer takes place from TiC(001) surface to the adsorbed Pt{sub n} clusters, resulting in the negatively charged Pt{sub n} clusters. At last, the d-band centers of the absorbed Pt atoms and their implications in the catalytic activity are discussed.« less

Spectroscopic determination of fundamental parameters of small angular diameter galactic open clusters

NASA Astrophysics Data System (ADS)

Ahumada, A. V.; Claria, J. J.; Bica, E.; Parisi, M. C.; Torres, M. C.; Pavani, D. B.

We present integrated spectra obtained at CASLEO (Argentina) for 9 galactic open clusters of small angular diameter. Two of them (BH 55 and Rup 159) have not been the target of previous research. The flux-calibrated spectra cover the spectral range approx. 3600-6900 A. Using the equivalent widths (EWs) of the Balmer lines and comparing the cluster spectra with template spectra, we determined E(B-V) colour excesses and ages for the present cluster sample. The parameters obtained for 6 of the clusters show good agreement with previous determinations based mainly on photometric methods. This is not the case, however, for BH 90, a scarcely reddened cluster, for which Moffat and Vogt (1975, Astron. and Astroph. SS, 20, 125) derived E(B-V) = 0.51. We explain and justify the strong discrepancy found for this object. According to the present analysis, 3 clusters are very young (Bo 14, Tr 15 and Tr 27), 2 are moderately young (NGC 6268 and BH 205), 3 are Hyades-like clusters (Rup 164, BH 90 and BH 55) and only one is an intermediate-age cluster (Rup 159).

Dual shell-like magnetic clusters containing Ni(II) and Ln(III) (Ln = La, Pr, and Nd) ions.

PubMed

Kong, Xiang-Jian; Ren, Yan-Ping; Long, La-Sheng; Zheng, Zhiping; Nichol, Gary; Huang, Rong-Bin; Zheng, Lan-Sun

2008-04-07

Dual shell-like nanoscopic magnetic clusters featuring a polynuclear nickel(II) framework encapsulating that of lanthanide ions (Ln = La, Pr, and Nd) were synthesized using Ni(NO3)(2).6H2O, Ln(NO3)(3).6H2O, and iminodiacetic acid (IDA) under hydrothermal conditions. Structurally established by crystallographic studies, these clusters are [La20Ni30(IDA)30(CO3)6(NO3)6(OH)30(H2O)12](CO3)(6).72H2O (1), [Ln20Ni21(C4H5NO4)21(OH)24(C2H2O3)6(C2O4)3(NO3)9(H2O)12](NO3)9.nH2O [C2H2O3 is the alkoxide form of glycolate; Ln = Pr (2), n = 42; Nd (3), n = 50], and {[La4Ni5Na(IDA)5(CO3)(NO3)4(OH)5(H2O)5][CO3].10H2O} infinity (4). Carbonate, oxalate, and glycolate are products of hydrothermal decomposition of IDA. Compositions of these compounds were confirmed by satisfactory elemental analyses. It has been found that the cluster structure is dependent on the identity of the lanthanide ion as well as the starting Ln/Ni/IDA ratio. The cationic cluster of 1 features a core of the Keplerate type with an outer icosidodecahedron of Ni(II) ions encaging a dodecahedral kernel of La(III). Clusters 2 and 3, distinctly different from 1, are isostructural, possessing a core of an outer shell of 21 Ni(II) ions encapsulating an inner shell of 20 Ln(III) ions. Complex 4 is a three-dimensional assembly of cluster building blocks connected by units of Na(NO3)/La(NO3)3; the structure of the building block resembles closely that of 1, with a hydrated La(III) ion internalized in the decanuclear cage being an extra feature. Magnetic studies indicated ferromagnetic interactions in 1, while overall antiferromagnetic interactions were revealed for 2 and 3. The polymeric, three-dimensional cluster network 4 displayed interesting ferrimagnetic interactions.

Internal velocity and mass distributions in simulated clusters of galaxies for a variety of cosmogonic models

NASA Technical Reports Server (NTRS)

Cen, Renyue

1994-01-01

The mass and velocity distributions in the outskirts (0.5-3.0/h Mpc) of simulated clusters of galaxies are examined for a suite of cosmogonic models (two Omega(sub 0) = 1 and two Omega(sub 0) = 0.2 models) utilizing large-scale particle-mesh (PM) simulations. Through a series of model computations, designed to isolate the different effects, we find that both Omega(sub 0) and P(sub k) (lambda less than or = 16/h Mpc) are important to the mass distributions in clusters of galaxies. There is a correlation between power, P(sub k), and density profiles of massive clusters; more power tends to point to the direction of a stronger correlation between alpha and M(r less than 1.5/h Mpc); i.e., massive clusters being relatively extended and small mass clusters being relatively concentrated. A lower Omega(sub 0) universe tends to produce relatively concentrated massive clusters and relatively extended small mass clusters compared to their counterparts in a higher Omega(sub 0) model with the same power. Models with little (initial) small-scale power, such as the hot dark matter (HDM) model, produce more extended mass distributions than the isothermal distribution for most of the mass clusters. But the cold dark matter (CDM) models show mass distributions of most of the clusters more concentrated than the isothermal distribution. X-ray and gravitational lensing observations are beginning providing useful information on the mass distribution in and around clusters; some interesting constraints on Omega(sub 0) and/or the (initial) power of the density fluctuations on scales lambda less than or = 16/h Mpc (where linear extrapolation is invalid) can be obtained when larger observational data sets, such as the Sloan Digital Sky Survey, become available.

Sodium abundances of AGB and RGB stars in Galactic globular clusters. II. Analysis and results of NGC 104, NGC 6121, and NGC 6809

NASA Astrophysics Data System (ADS)

Wang, Y.; Primas, F.; Charbonnel, C.; Van der Swaelmen, M.; Bono, G.; Chantereau, W.; Zhao, G.

2017-11-01

Aims: We investigate the Na abundance distribution of asymptotic giant branch (AGB) stars in Galactic globular clusters (GCs) and its possible dependence on GC global properties, especially age and metallicity. Methods: We analyze high-resolution spectra of a large sample of AGB and red giant branch (RGB) stars in the Galactic GCs NGC 104, NGC 6121, and NGC 6809 obtained with FLAMES/GIRAFFE at ESO/VLT, and determine their Na abundances. This is the first time that the AGB stars in NGC 6809 are targeted. Moreover, to investigate the dependence of AGB Na abundance dispersion on GC parameters, we compare the AGB [Na/H] distributions of a total of nine GCs, with five determined by ourselves with homogeneous method and four from literature, covering a wide range of GC parameters. Results: NGC 104 and NGC 6809 have comparable AGB and RGB Na abundance distributions revealed by the K-S test, while NGC 6121 shows a lack of very Na-rich AGB stars. By analyzing all nine GCs, we find that the Na abundances and multiple populations of AGB stars form complex picture. In some GCs, AGB stars have similar Na abundances and/or second-population fractions as their RGB counterparts, while some GCs do not have Na-rich second-population AGB stars, and various cases exist between the two extremes. In addition, the fitted relations between fractions of the AGB second population and GC global parameters show that the AGB second-population fraction slightly anticorrelates with GC central concentration, while no robust dependency can be confirmed with other GC parameters. Conclusions: Current data roughly support the prediction of the fast-rotating massive star (FRMS) scenario. However, considering the weak observational and theoretical trends where scatter and exceptions exist, the fraction of second-population AGB stars can be affected by more than one or two factors, and may even be a result of stochasticity. Based on observations made with ESO telescopes at the La Silla Paranal Observatory under programme ID 093.D-0818(A).Full Tables 3, 5, and 7 are 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/607/A135

Coupled multipolar interactions in small-particle metallic clusters.

PubMed

Pustovit, Vitaly N; Sotelo, Juan A; Niklasson, Gunnar A

2002-03-01

We propose a new formalism for computing the optical properties of small clusters of particles. It is a generalization of the coupled dipole-dipole particle-interaction model and allows one in principle to take into account all multipolar interactions in the long-wavelength limit. The method is illustrated by computations of the optical properties of N = 6 particle clusters for different multipolar approximations. We examine the effect of separation between particles and compare the optical spectra with the discrete-dipole approximation and the generalized Mie theory.

A Wsbnd Ne interatomic potential for simulation of neon implantation in tungsten

NASA Astrophysics Data System (ADS)

Backman, Marie; Juslin, Niklas; Huang, Guiyang; Wirth, Brian D.

2016-08-01

An interatomic pair potential for Wsbnd Ne is developed for atomistic molecular dynamics simulations of neon implantation in tungsten. The new potential predicts point defect energies and binding energies of small clusters that are in good agreement with electronic structure calculations. Molecular dynamics simulations of small neon clusters in tungsten show that trap mutation, in which an interstitial neon cluster displaces a tungsten atom from its lattice site, occurs for clusters of three or more neon atoms. However, near a free surface, trap mutation can occur at smaller sizes, including even a single neon interstitial in close proximity to a (100) or (110) surface.

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

NASA Astrophysics Data System (ADS)

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

2014-03-01

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

Relative dispersion of clustered drifters in a small micro-tidal estuary

NASA Astrophysics Data System (ADS)

Suara, Kabir; Chanson, Hubert; Borgas, Michael; Brown, Richard J.

2017-07-01

Small tide-dominated estuaries are affected by large scale flow structures which combine with the underlying bed generated smaller scale turbulence to significantly increase the magnitude of horizontal diffusivity. Field estimates of horizontal diffusivity and its associated scales are however rare due to limitations in instrumentation. Data from multiple deployments of low and high resolution clusters of GPS-drifters are used to examine the dynamics of a surface flow in a small micro-tidal estuary through relative dispersion analyses. During the field study, cluster diffusivity, which combines both large- and small-scale processes ranged between, 0.01 and 3.01 m2/s for spreading clusters and, -0.06 and -4.2 m2/s for contracting clusters. Pair-particle dispersion, Dp2, was scale dependent and grew as Dp2 ∼ t1.83 in streamwise and Dp2 ∼ t0.8 in cross-stream directions. At small separation scale, pair-particle (d < 0.5 m) relative diffusivity followed the Richardson's 4/3 power law and became weaker as separation scale increases. Pair-particle diffusivity was described as Kp ∼ d1.01 and Kp ∼ d0.85 in the streamwise and cross-stream directions, respectively for separation scales ranging from 0.1 to 10 m. Two methods were used to identify the mechanism responsible for dispersion within the channel. The results clearly revealed the importance of strain fields (stretching and shearing) in the spreading of particles within a small micro-tidal channel. The work provided input for modelling dispersion of passive particle in shallow micro-tidal estuaries where these were not previously experimentally studied.

Proteome Analyses of Hydrogen-producing Hyperthermophilic Archaeon Thermococcus onnurineus NA1 in Different One-carbon Substrate Culture Conditions*

PubMed Central

Moon, Yoon-Jung; Kwon, Joseph; Yun, Sung-Ho; Lim, Hye Li; Kim, Min-Sik; Kang, Sung Gyun; Lee, Jung-Hyun; Choi, Jong-Soon; Kim, Seung Il; Chung, Young-Ho

2012-01-01

Thermococcus onnurineus NA1, a sulfur-reducing hyperthermophilic archaeon, is capable of H2-producing growth, considered to be hydrogenogenic carboxydotrophy. Utilization of formate as a sole energy source has been well studied in T. onnurineus NA1. However, whether formate can be used as its carbon source remains unknown. To obtain a global view of the metabolic characteristics of H2-producing growth, a quantitative proteome analysis of T. onnurineus NA1 grown on formate, CO, and starch was performed by combining one-dimensional SDS-PAGE with nano UPLC-MSE. A total of 587 proteins corresponding to 29.7% of the encoding genes were identified, and the major metabolic pathways (especially energy metabolism) were characterized at the protein level. Expression of glycolytic enzymes was common but more highly induced in starch-grown cells. In contrast, enzymes involved in key steps of the gluconeogenesis and pentose phosphate pathways were strongly up-regulated in formate-grown cells, suggesting that formate could be utilized as a carbon source by T. onnurineus NA1. In accordance with the genomic analysis, comprehensive proteomic analysis also revealed a number of hydrogenase clusters apparently associated with formate metabolism. On the other hand, CODH and CO-induced hydrogenases belonging to the Hyg4-II cluster, as well as sulfhydrogenase-I and Mbx, were prominently expressed during CO culture. Our data suggest that CO can be utilized as a sole energy source for H2 production via an electron transport mechanism and that CO2 produced from catabolism or CO oxidation by CODH and CO-induced hydrogenases may subsequently be assimilated into the organic carbon. Overall, proteomic comparison of formate- and CO-grown cells with starch-grown cells revealed that a single carbon compound, such as formate and CO, can be utilized as an efficient substrate to provide cellular carbon and/or energy by T. onnurineus NA1. PMID:22232491

Critical behavior of the contact process on small-world networks

NASA Astrophysics Data System (ADS)

Ferreira, Ronan S.; Ferreira, Silvio C.

2013-11-01

We investigate the role of clustering on the critical behavior of the contact process (CP) on small-world networks using the Watts-Strogatz (WS) network model with an edge rewiring probability p. The critical point is well predicted by a homogeneous cluster-approximation for the limit of vanishing clustering ( p → 1). The critical exponents and dimensionless moment ratios of the CP are in agreement with those predicted by the mean-field theory for any p > 0. This independence on the network clustering shows that the small-world property is a sufficient condition for the mean-field theory to correctly predict the universality of the model. Moreover, we compare the CP dynamics on WS networks with rewiring probability p = 1 and random regular networks and show that the weak heterogeneity of the WS network slightly changes the critical point but does not alter other critical quantities of the model.

A comparison of confidence interval methods for the intraclass correlation coefficient in community-based cluster randomization trials with a binary outcome.

PubMed

Braschel, Melissa C; Svec, Ivana; Darlington, Gerarda A; Donner, Allan

2016-04-01

Many investigators rely on previously published point estimates of the intraclass correlation coefficient rather than on their associated confidence intervals to determine the required size of a newly planned cluster randomized trial. Although confidence interval methods for the intraclass correlation coefficient that can be applied to community-based trials have been developed for a continuous outcome variable, fewer methods exist for a binary outcome variable. The aim of this study is to evaluate confidence interval methods for the intraclass correlation coefficient applied to binary outcomes in community intervention trials enrolling a small number of large clusters. Existing methods for confidence interval construction are examined and compared to a new ad hoc approach based on dividing clusters into a large number of smaller sub-clusters and subsequently applying existing methods to the resulting data. Monte Carlo simulation is used to assess the width and coverage of confidence intervals for the intraclass correlation coefficient based on Smith's large sample approximation of the standard error of the one-way analysis of variance estimator, an inverted modified Wald test for the Fleiss-Cuzick estimator, and intervals constructed using a bootstrap-t applied to a variance-stabilizing transformation of the intraclass correlation coefficient estimate. In addition, a new approach is applied in which clusters are randomly divided into a large number of smaller sub-clusters with the same methods applied to these data (with the exception of the bootstrap-t interval, which assumes large cluster sizes). These methods are also applied to a cluster randomized trial on adolescent tobacco use for illustration. When applied to a binary outcome variable in a small number of large clusters, existing confidence interval methods for the intraclass correlation coefficient provide poor coverage. However, confidence intervals constructed using the new approach combined with Smith's method provide nominal or close to nominal coverage when the intraclass correlation coefficient is small (<0.05), as is the case in most community intervention trials. This study concludes that when a binary outcome variable is measured in a small number of large clusters, confidence intervals for the intraclass correlation coefficient may be constructed by dividing existing clusters into sub-clusters (e.g. groups of 5) and using Smith's method. The resulting confidence intervals provide nominal or close to nominal coverage across a wide range of parameters when the intraclass correlation coefficient is small (<0.05). Application of this method should provide investigators with a better understanding of the uncertainty associated with a point estimator of the intraclass correlation coefficient used for determining the sample size needed for a newly designed community-based trial. © The Author(s) 2015.

Dating star clusters in the Small Magellanic Cloud by means of integrated spectra

NASA Astrophysics Data System (ADS)

Ahumada, A. V.; Clariá, J. J.; Bica, E.; Dutra, C. M.

2002-10-01

In this study flux-calibrated integrated spectra in the range (3600-6800) Å are presented for 16 concentrated star clusters in the Small Magellanic Cloud (SMC), approximately half of which constitute unstudied objects. We have estimated ages and foreground interstellar reddening values from the comparison of the line strengths and continuum distribution of the cluster spectra with those of template cluster spectra with known parameters. Most of the sample clusters are young blue clusters (6-50 Myr), while L 28, NGC 643 and L 114 are found to be intermediate-age clusters (1-6 Gyr). One well known SMC cluster (NGC 416) was observed for comparison purposes. The sample includes clusters in the surroundings and main body of the SMC, and the derived foreground reddening values are in the range 0.00 <= E(B-V) <= 0.15. The present data also make up a cluster spectral library at SMC metallicity. Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan, Argentina.

Solvation of Na^+ in water from first-principles molecular dynamics

NASA Astrophysics Data System (ADS)

White, J. A.; Schwegler, E.; Galli, G.; Gygi, F.

2000-03-01

We have carried out ab initio molecular dynamics (MD) simulations of the Na^+ ion in water with an MD cell containing a single alkali ion and 53 water molecules. The electron-electron and electron-ion interactions were modeled by density functional theory with a generalized gradient approximation for the exchange-correlation functional. The computed radial distribution functions, coordination numbers, and angular distributions are consistent with available experimental data. The first solvation shell contains 5.2±0.6 water molecules, with some waters occasionally exchanging with those of the second shell. The computed Na^+ hydration number is larger than that from calculations for water clusters surrounding an Na^+ ion, but is consistent with that derived from x-ray measurements. Our results also indicate that the first hydration shell is better defined for Na^+ than for K^+ [1], as indicated by the first minimum in the Na-O pair distribution function. [1] L.M. Ramaniah, M. Bernasconi, and M. Parrinello, J. Chem. Phys. 111, 1587 (1999). This work was performed for DOE under contract W-7405-ENG-48.

Na+/K+ ATPase regulates the expression and localization of acetylcholine receptors in a pump activity-independent manner

PubMed Central

Doi, Motomichi; Iwasaki, Kouichi

2008-01-01

Na+/K+ ATPase is a plasma membrane-localized sodium pump that maintains the ion gradients between the extracellular and intracellular environments, which in turn controls the cellular resting membrane potential. Recent evidence suggests that the pump is also localized at synapses and regulates synaptic efficacy. However, its precise function at the synapse is unknown. Here we show that two mutations in the α subunit of the eat-6 Na+/K+ ATPase in Caenorhabditis elegans dramatically increase the sensitivity to acetylcholine (Ach) agonists and alter the localization of nicotinic Ach receptors at the neuromuscular junction (NMJ). These defects can be rescued by mutated EAT-6 proteins which lack its pump activity, suggesting the presence of a novel function for Ach signaling. The Na+/K+ ATPase accumulates at postsynaptic sites and appears to surround Ach receptors to maintain rigid clusters at the NMJ. Our findings suggest a critical pump activity-independent, allele –specific role for Na+/K+ ATPase on postsynaptic organization and synaptic efficacy. PMID:18599311

Reconsideration on Hydration of Sodium Ion: From Micro-Hydration to Bulk Hydration

NASA Astrophysics Data System (ADS)

Yongquan, Zhou; Chunhui, Fang; Yan, Fang; Fayan, Zhu; Haiwen, Ge; Hongyan, Liu

2017-12-01

Micro hydration structures of the sodium ion, [Na(H2O) n ]+, n = 1-12, were probed by density functional theory (DFT) at B3LYP/aug-cc-pVDZ level in both gaseous and aqueous phase. The predicted equilibrium sodium-oxygen distance of 0.240 nm at the present level of theory. The four-, five- and six-coordinated cluster can transform from each other at the ambient condition. The analysis of the successive water binding energy and natural charge population (NBO) on Na+ clearly shows that the influence of Na+ on the surrounding water molecules goes beyond the first hydration shell with the hydration number of 6. The Car-Parrinello molecular dynamic simulation shows that only the first hydration sphere can be found, and the hydration number of Na+ is 5.2 and the hydration distance ( r Na-O) is 0.235 nm. All our simulations mentioned in the present paper show an excellent agreement with the diffraction result from X-ray scattering study.

Groundwater flow processes and mixing in active volcanic systems: the case of Guadalajara (Mexico)

NASA Astrophysics Data System (ADS)

Hernández-Antonio, A.; Mahlknecht, J.; Tamez-Meléndez, C.; Ramos-Leal, J.; Ramírez-Orozco, A.; Parra, R.; Ornelas-Soto, N.; Eastoe, C. J.

2015-02-01

Groundwater chemistry and isotopic data from 40 production wells in the Atemajac and Toluquilla Valleys, located in and around the Guadalajara metropolitan area, were determined to develop a conceptual model of groundwater flow processes and mixing. Multivariate analysis including cluster analysis and principal component analysis were used to elucidate distribution patterns of constituents and factors controlling groundwater chemistry. Based on this analysis, groundwater was classified into four groups: cold groundwater, hydrothermal water, polluted groundwater and mixed groundwater. Cold groundwater is characterized by low temperature, salinity, and Cl and Na concentrations and is predominantly of Na-HCO3 type. It originates as recharge at Primavera caldera and is found predominantly in wells in the upper Atemajac Valley. Hydrothermal water is characterized by high salinity, temperature, Cl, Na, HCO3, and the presence of minor elements such as Li, Mn and F. It is a mixed HCO3 type found in wells from Toluquilla Valley and represents regional flow circulation through basaltic and andesitic rocks. Polluted groundwater is characterized by elevated nitrate and sulfate concentrations and is usually derived from urban water cycling and subordinately from agricultural practices. Mixed groundwaters between cold and hydrothermal components are predominantly found in the lower Atemajac Valley. Tritium method elucidated that practically all of the sampled groundwater contains at least a small fraction of modern water. The multivariate mixing model M3 indicates that the proportion of hydrothermal fluids in sampled well water is between 13 (local groundwater) and 87% (hydrothermal water), and the proportion of polluted water in wells ranges from 0 to 63%. This study may help local water authorities to identify and quantify groundwater contamination and act accordingly.

Salt Intake and the Association with Blood Pressure in Young Iranian Children: First Report From the Middle East and North Africa

PubMed Central

Kelishadi, Roya; Gheisari, Alaleh; Zare, Narges; Farajian, Sanam; Shariatinejad, Keyvan

2013-01-01

Background: This study aimed to assess the salt intake of Iranian children, and to assess the correlation of urinary electrolytes excretion with blood pressure. Methods: This cross-sectional study was conducted in 2011-2012 among 3-10-year-old children, selected by multi-stage cluster sampling from urban and rural areas of Isfahan, Iran. The sodium (Na), potassium (K), and creatinine (Cr) were measured in a random sample of the children's first morning fasting urine. Three-day averages of dietary intakes were analyzed by the Nutritionist-4 software. Results: The mean (SD) of urinary Na was 177.17 (28.68) mEq/day without significant difference according to gender and living area. The mean (SD) dietary intakes of Na and K were 2017.76 (117.94) and 1119.06 (76.03) mg/day, respectively. Children of urban and rural areas consumed similar sources of salty foods (bread, cheese, and snacks) and had low intake of vegetables. No significant association was documented between urinary electrolytes excretions and blood pressure. Conclusions: This study, which to the best of our knowledge is the first of its kind in the Middle East and North Africa region, revealed that Iranian young children consume a large amount of sodium and small amount of potassium. The non-significant associations of electrolyte excretions with blood pressure may be because of the very young age group of participants. Given the development of preference to salt taste from early childhood, and the tracking of risk factors of chronic diseases from this age, reducing salt intake of young children should be emphasized. PMID:23671781

Effect of Self-Assembly of Fullerene Nano-Particles on Lipid Membrane

PubMed Central

Zhang, Saiqun; Mu, Yuguang; Zhang, John Z. H.; Xu, Weixin

2013-01-01

Carbon nanoparticles can penetrate the cell membrane and cause cytotoxicity. The diffusion feature and translocation free energy of fullerene through lipid membranes is well reported. However, the knowledge on self-assembly of fullerenes and resulting effects on lipid membrane is poorly addressed. In this work, the self-assembly of fullerene nanoparticles and the resulting influence on the dioleoylphosphtidylcholine (DOPC) model membrane were studied by using all-atom molecular dynamics simulations with explicit solvents. Our simulation results confirm that gathered small fullerene cluster can invade lipid membrane. Simulations show two pathways: 1) assembly process is completely finished before penetration; 2) assembly process coincides with penetration. Simulation results also demonstrate that in the membrane interior, fullerene clusters tend to stay at the position which is 1.0 nm away from the membrane center. In addition, the diverse microscopic stacking mode (i.e., equilateral triangle, tetrahedral pentahedral, trigonal bipyramid and octahedron) of these small fullerene clusters are well characterized. Thus our simulations provide a detailed high-resolution characterization of the microscopic structures of the small fullerene clusters. Further, we found the gathered small fullerene clusters have significant adverse disturbances to the local structure of the membrane, but no great influence on the global integrity of the lipid membrane, which suggests the prerequisite of high-content fullerene for cytotoxicity. PMID:24204827

Effects of molecular weight and cationization agent on the sensitivity of Bi cluster secondary ion mass spectrometry.

PubMed

Fujii, Makiko; Shishido, Rie; Satoh, Takaya; Suzuki, Shigeru; Matsuo, Jiro

2016-07-30

Bi cluster secondary ion mass spectrometry (SIMS) is one of the most promising tools for precise analysis of synthetic polymers. However, the sensitivity in the high-mass region is still insufficient compared with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). Accordingly, the effects of metal assistance (cationization agents) were investigated in this study. To investigate the effects caused by varying the ionization agent, three different polyethylene glycol (PEG) samples were prepared, one with an Ag-deposited film, and two others mixed with Ag and Na, respectively. The measurements were performed by using a commercial Bi cluster SIMS and MALDI-TOFMS systems. The mass spectrum obtained with MALDI-TOFMS was used as a reference molecular weight distribution to evaluate the effects of molecular weight and primary ion species (Bi + , Bi 3 + , Bi 3 2 + ) on the sensitivity of Bi cluster SIMS. The intensity of each secondary ion was the highest in Bi 3 2 + irradiation, and the lowest in Bi + irradiation. Regarding the cationization agents, the secondary ion yield was the highest for the sample mixed with Ag, while the degree of decay of sensitivity along with the increase in molecular weight was the smallest for the sample mixed with Na. It was suggested that the cationization mechanism consists of pre-formed ionization and gas-phase ionization processes. The sensitivity of Bi cluster SIMS decreases to approximately one-fiftieth in every 1000 u. These results might help in understanding the mechanism of cationization and further enhancement of secondary ion yields of polymers. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

The CNO Bi-cycle in the Open Cluster NGC 752

NASA Astrophysics Data System (ADS)

Hawkins, Keith; Schuler, S.; King, J.; The, L.

2011-01-01

The CNO bi-cycle is the primary energy source for main sequence stars more massive than the sun. To test our understanding of stellar evolution models using the CNO bi-cycle, we have undertaken light-element (CNO) abundance analysis of three main sequence dwarf stars and three red giant stars in the open cluster NGC 752 utilizing high resolution (R 50,000) spectroscopy from the Keck Observatory. Preliminary results indicate, as expected, there is a depletion of carbon in the giants relative to the dwarfs. Additional analysis is needed to determine if the amount of depletion is in line with model predictions, as seen in the Hyades open cluster. Oxygen abundances are derived from the high-excitation O I triplet, and there is a 0.19 dex offset in the [O/H] abundances between the giants and dwarfs which may be explained by non-local thermodynamic equilibrium (NLTE), although further analysis is needed to verify this. The standard procedure for spectroscopically determining stellar parameters used here allows for a measurement of the cluster metallicity, [Fe/H] = 0.04 ± 0.02. In addition to the Fe abundances we have determined Na, Mg, and Al abundances to determine the status of other nucleosynthesis processes. The Na, Mg and Al abundances of the giants are enhanced relative to the dwarfs, which is consistent with similar findings in giants of other open clusters. Support for K. Hawkins was provided by the NOAO/KPNO Research Experiences for Undergraduates (REU) Program which is funded by the National Science Foundation Research Experiences for Undergraduates Program and the Department of Defense ASSURE program through Scientific Program Order No. 13 (AST-0754223) of the Cooperative Agreement No. AST-0132798 between the Association of Universities for Research in Astronomy (AURA) and the NSF.

The origin of low mass particles within and beyond the dust coma envelopes of Comet Halley

NASA Technical Reports Server (NTRS)

Simpson, J. A.; Rabinowitz, D.; Tuzzolino, A. J.; Ksanfomality, L. V.; Sagdeev, R. Z.

1987-01-01

Measurements from the Dust Counter and Mass Analyzer (DUCMA) instruments on VEGA-1 and -2 revealed unexpected fluxes of low mass (up to 10 to the minus 13th power g) dust particles at very great distances from the nucleus (300,000 to 600,000 km). These particles are detected in clusters (10 sec duration), preceded and followed by relatively long time intervals during which no dust is detected. This cluster phenomenon also occurs inside the envelope boundaries. Clusters of low mass particles are intermixed with the overall dust distribution throughout the coma. The clusters account for many of the short-term small-scale intensity enhancements previously ascribed to microjets in the coma. The origin of these clusters appears to be emission from the nucleus of large conglomerates which disintegrate in the coma to yield clusters of discrete, small particles continuing outward to the distant coma.

Equilibrium geometries, electronic and magnetic properties of small AunNi- (n = 1-9) clusters

NASA Astrophysics Data System (ADS)

Tang, Cui-Ming; Chen, Xiao-Xu; Yang, Xiang-Dong

2014-05-01

Geometrical, electronic and magnetic properties of small AunNi- (n = 1-9) clusters have been investigated based on density functional theory (DFT) at PW91P86 level. An extensive structural search shows that the relative stable structures of AunNi- (n = 1-9) clusters adopt 2D structure for n = 1-5, 7 and 3D structure for n = 6, 8-9. And the substitution of a Ni atom for an Au atom in the Au-n+1 cluster obviously changes the structure of the host cluster. Moreover, an odd-even alternation phenomenon has been found for HOMO-LUMO energy gaps, indicating that the relative stable structures of the AunNi- clusters with odd-numbered gold atoms have a higher relative stability. Finally, the natural population analysis (NPA) and the vertical detachment energies (VDE) are studied, respectively. The theoretical values of VDE are reported for the first time to our best knowledge.

Thermodynamic properties of small aggregates of rare-gas atoms

NASA Technical Reports Server (NTRS)

Etters, R. D.; Kaelberer, J.

1975-01-01

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

Mixing state of ambient aerosols during different fog-haze pollution episodes in the Yangtze River Delta, China

NASA Astrophysics Data System (ADS)

Hu, Rui; Wang, Honglei; Yin, Yan; Chen, Kui; Zhu, Bin; Zhang, Zefeng; Kang, Hui; Shen, Lijuan

2018-04-01

The mixing state of aerosol particles were investigated using a single particle aerosol mass spectrometer (SPAMS) during a regional fog-haze episode in the Yangtze River Delta (YRD) on 16-28 Dec., 2015. The aerosols were analyzed and clustered into 12 classes: aged elemental carbon (Aged-EC), internally mixed organics and elemental carbon (ECOC), organic carbon (OC), Biomass, Amine, Ammonium, Na-K, V-rich, Pb-rich, Cu-rich, Fe-rich and Dust. Results showed that particles in short-term rainfalls mixed with more nitrate and oxidized organics, while they mixed with more ammonium and sulfate in long-term rainfall. Due to anthropogenic activities, stronger winds and solar radiation, the particle counts increased and the size ranges of particles broadened in haze. Carbonaceous particles and Na-K mixed with enhanced secondary species during haze, and obviously were more acidic, especially for the ones with a size range of 0.6-1.2 μm. For local and long-range transported pollution, OC had distinct size distributions while the changes of ECOC were uniform. The secondary formation of ECOC contributed significantly in local pollution and affected much smaller particles (as small as 0.5 μm) in long-range transported pollution. And long-range transported pollution was more helpful for the growth of OC. Particles mixed with more chloride and nitrate/sulfate in local/long-range transported pollution.

Low-resolution spectroscopy of main sequence stars belonging to 12 Galactic globular clusters. I. CH and CN band strength variations

NASA Astrophysics Data System (ADS)

Pancino, E.; Rejkuba, M.; Zoccali, M.; Carrera, R.

2010-12-01

Context. Globular clusters show star-to-star abundance variations for light elements that are not yet well understood. The preferred explanation involves a self-enrichment scenario, within which two subsequent generations of stars co-exist in globular clusters. Observations of chemical abundances in the main sequence and sub-giant branch stars allow us to investigate the signature of this chemically processed material without the complicating effects caused by stellar evolution and internal mixing. Aims: Our main goal is to investigate the carbon-nitrogen anti-correlation with low-resolution spectroscopy of 20-50 stars fainter than the first dredge-up in seven Galactic globular clusters (NGC 288, NGC 1851, NGC 5927, NGC 6352, NGC 6388, and Pal 12) with different properties. We complemented our observations with 47 Tuc archival data, with four additional clusters from the literature (M 15, M 22, M 55, NGC 362), and with additional literature data on NGC 288. Methods: In this first paper, we measured the strengh of the CN and CH band indices, which correlate with the N and C abundances, and we investigated the anti-correlation and bimodality of these indices. We compared rCN, the ratio of stars belonging to the CN-strong and weak groups, with 15 different cluster parameters. Results: We clearly see bimodal anti-correlation of the CH and CN band stregths in the metal-rich clusters (Pal 12, 47 Tuc, NGC 6352, NGC 5927). Only M 15 among the metal-poor clusters shows a clearly bimodal anti-correlation. We found weak correlations (sligthly above 1σ) of rCN with the cluster orbital parameters, present-day total mass, cluster concentration, and age. Conclusions: Our findings support the self-enrichment scenario, and suggest that the occurrence of more than two major generations of stars in a GGC should be rare. Small additional generations (<10-20% of the total) would be difficult to detect with our samples. The first generation, which corresponds to the CN-weak stars, usually contains more stars than the second one ( = 0.82±0.29), as opposed to results based on the Na-O anti-correlations. Based on FORS observations collected at the European Southern Observatory, Chile, within the observing programs 68.D-0510 and 69.D-0056. Also based on data obtained from the ESO Archive, within the observing program 67.D-0153.Complete Table 2 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/524/A44

2D Electrides as Promising Anode Materials for Na-Ion Batteries from First-Principles Study.

PubMed

Hu, Junping; Xu, Bo; Yang, Shengyuan A; Guan, Shan; Ouyang, Chuying; Yao, Yugui

2015-11-04

Searching for suitable anodes with good performance is a key challenge for rechargeable Na-ion batteries (NIBs). Using the first-principles method, we predict that 2D nitrogen electride materials can be served as anode materials for NIBs. Particularly, we show that Ca2N meets almost all the requirements of a good NIB anode. Each formula unit of a monolayer Ca2N sheet can absorb up to four Na atoms, corresponding to a theoretical specific capacity of 1138 mAh·g(-1). The metallic character for both pristine Ca2N and its Na intercalated state NaxCa2N ensures good electronic conduction. Na diffusion along the 2D monolayer plane can be very fast even at room temperature, with a Na migration energy barrier as small as 0.084 eV. These properties are key to the excellent rate performance of an anode material. The average open-circuit voltage is calculated to be 0.18 V vs Na/Na(+) for the chemical stoichiometry of Na2Ca2N and 0.09 V for Na4Ca2N. The relatively low average open-circuit voltage is beneficial to the overall voltage of the cell. In addition, the 2D monolayers have very small lattice change upon Na intercalation, which ensures a good cycling stability. All these results demonstrate that the Ca2N monolayer could be an excellent anode material for NIBs.

Localization and Function of the Membrane-bound Riboflavin in the Na+-translocating NADH:Quinone Oxidoreductase (Na+-NQR) from Vibrio cholerae*

PubMed Central

Casutt, Marco S.; Huber, Tamara; Brunisholz, René; Tao, Minli; Fritz, Günter; Steuber, Julia

2010-01-01

The sodium ion-translocating NADH:quinone oxidoreductase (Na+-NQR) from the human pathogen Vibrio cholerae is a respiratory membrane protein complex that couples the oxidation of NADH to the transport of Na+ across the bacterial membrane. The Na+-NQR comprises the six subunits NqrABCDEF, but the stoichiometry and arrangement of these subunits are unknown. Redox-active cofactors are FAD and a 2Fe-2S cluster on NqrF, covalently attached FMNs on NqrB and NqrC, and riboflavin and ubiquinone-8 with unknown localization in the complex. By analyzing the cofactor content and NADH oxidation activity of subcomplexes of the Na+-NQR lacking individual subunits, the riboflavin cofactor was unequivocally assigned to the membrane-bound NqrB subunit. Quantitative analysis of the N-terminal amino acids of the holo-complex revealed that NqrB is present in a single copy in the holo-complex. It is concluded that the hydrophobic NqrB harbors one riboflavin in addition to its covalently attached FMN. The catalytic role of two flavins in subunit NqrB during the reduction of ubiquinone to ubiquinol by the Na+-NQR is discussed. PMID:20558724

Na+-independent transporters, LAT-2 and b0,+, exchange L-DOPA with neutral and basic amino acids in two clonal renal cell lines.

PubMed

Gomes, P; Soares-da-Silva, P

2002-03-15

The present study examined the functional characteristics of L-DOPA transporters in two functionally different clonal subpopulations of opossum kidney (OKLC and OKHC) cells. The uptake of L-DOPA was largely Na+-independent, though in OKHC cells a minor component (approximately 15%) required extracellular Na+. At least two Na+-independent transporters appear to be involved in L-DOPA uptake. One of these transporters has a broad specificity for small and large neutral amino acids, is stimulated by acid pH and inhibited by 2-aminobicyclo(2,2,l)-heptane-2-carboxylic acid (BCH; OKLC, Ki = 291 mM; OKHC, Ki = 380 mM). The other Na+-independent transporter binds neutral and basic amino acids and also recognizes the di-amino acid cystine. [14C]-L-DOPA efflux from OKLC and OKHC cells over 12 min corresponded to a small amount of intracellular [14C]-L-DOPA. L-Leucine, nonlabelled L-DOPA, BCH and L-arginine, stimulated the efflux of [14C]-L-DOPA in a Na+-independent manner. It is suggested that L-DOPA uses at least two major transporters, systems LAT-2 and b0,+. The transport of L-DOPA by LAT-2 corresponds to a Na+-independent transporter with a broad specificity for small and large neutral amino acids, stimulated by acid pH and inhibited by BCH. The transport of L-DOPA by system b0,+ is a Na+-independent transporter for neutral and basic amino acids that also recognizes cystine. LAT-2 was found equally important at the apical and basolateral membranes, whereas system b0,+ had a predominant distribution in apical membranes.

Thiolate-bridged dinuclear iron(tris-carbonyl)–nickel complexes relevant to the active site of [NiFe] hydrogenase

PubMed Central

Ohki, Yasuhiro; Yasumura, Kazunari; Kuge, Katsuaki; Tanino, Soichiro; Ando, Masaru; Li, Zilong; Tatsumi, Kazuyuki

2008-01-01

The reaction of NiBr2(EtOH)4 with a 1:2–3 mixture of FeBr2(CO)4 and Na(SPh) generated a linear trinuclear Fe–Ni–Fe cluster (CO)3Fe(μ-SPh)3Ni(μ-SPh)3Fe(CO)3, 1, whereas the analogous reaction system FeBr2(CO)4/Na(StBu)/NiBr2(EtOH)4 (1:2–3:1) gave rise to a linear tetranuclear Fe–Ni–Ni–Fe cluster [(CO)3Fe(μ-StBu)3Ni(μ-Br)]2, 2. By using this tetranuclear cluster 2 as the precursor, we have developed a new synthetic route to a series of thiolate-bridged dinuclear Fe(CO)3–Ni complexes, the structures of which mimic [NiFe] hydrogenase active sites. The reactions of 2 with SC(NMe2)2 (tmtu), Na{S(CH2)2SMe} and ortho-NaS(C6H4)SR (R = Me, tBu) led to isolation of (CO)3Fe(μ-StBu)3NiBr(tmtu), 3, (CO)3Fe(StBu)(μ-StBu)2Ni{S(CH2)2SMe}, 4, and (CO)3Fe(StBu)(μ-StBu)2Ni{S(C6H4)SR}, 5a (R = Me) and 5b (R = tBu), respectively. On the other hand, treatment of 2 with 2-methylthio-phenolate (ortho-O(C6H4)SMe) in methanol resulted in (CO)3Fe(μ-StBu)3Ni(MeOH){O(C6H4)SMe}, 6a. The methanol molecule bound to Ni is labile and is readily released under reduced pressure to afford (CO)3Fe(StBu)(μ-StBu)2Ni{O(C6H4)SMe}, 6b, and the coordination geometry of nickel changes from octahedral to square planar. Likewise, the reaction of 2 with NaOAc in methanol followed by crystallization from THF gave (CO)3Fe(μ-StBu)3Ni(THF)(OAc), 7. The dinuclear complexes, 3-7, are thermally unstable, and a key to their successful isolation is to carry out the reactions and manipulations at −40°C. PMID:18511566

Extracting magnetic cluster size and its distributions in advanced perpendicular recording media with shrinking grain size using small angle x-ray scattering

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

Mehta, Virat; Ikeda, Yoshihiro; Takano, Ken

2015-05-18

We analyze the magnetic cluster size (MCS) and magnetic cluster size distribution (MCSD) in a variety of perpendicular magnetic recording (PMR) media designs using resonant small angle x-ray scattering at the Co L{sub 3} absorption edge. The different PMR media flavors considered here vary in grain size between 7.5 and 9.5 nm as well as in lateral inter-granular exchange strength, which is controlled via the segregant amount. While for high inter-granular exchange, the MCS increases rapidly for grain sizes below 8.5 nm, we show that for increased amount of segregant with less exchange the MCS remains relatively small, even for grain sizesmore » of 7.5 and 8 nm. However, the MCSD still increases sharply when shrinking grains from 8 to 7.5 nm. We show evidence that recording performance such as signal-to-noise-ratio on the spin stand correlates well with the product of magnetic cluster size and magnetic cluster size distribution.« less

A DFT study of the stability of SIAs and small SIA clusters in the vicinity of solute atoms in Fe

NASA Astrophysics Data System (ADS)

Becquart, C. S.; Ngayam Happy, R.; Olsson, P.; Domain, C.

2018-03-01

The energetics, defect volume and magnetic properties of single SIAs and small SIA clusters up to size 6 have been calculated by DFT for different configurations like the parallel 〈110〉 dumbbell, the non parallel 〈110〉 dumbbell and the C15 structure. The most stable configurations of each type have been further analyzed to determine the influence on their stability of various solute atoms (Ti, V, Cr, Mn, Co, Ni, Cu, Mo, W, Pd, Al, Si, P), relevant for steels used under irradiation. The results show that the presence of solute atoms does not change the relative stability order among SIA clusters. The small SIA clusters investigated can bind to both undersized and oversized solutes. Several descriptors have been considered to derive interesting trends from results. It appears that the local atomic volume available for the solute is the main physical quantity governing the binding energy evolution, whatever the solute type (undersized or oversized) and the cluster configuration (size and type).

Effects of manganese doping on the structure evolution of small-sized boron clusters

NASA Astrophysics Data System (ADS)

Zhao, Lingquan; Qu, Xin; Wang, Yanchao; Lv, Jian; Zhang, Lijun; Hu, Ziyu; Gu, Guangrui; Ma, Yanming

2017-07-01

Atomic doping of clusters is known as an effective approach to stabilize or modify the structures and properties of resulting doped clusters. We herein report the effect of manganese (Mn) doping on the structure evolution of small-sized boron (B) clusters. The global minimum structures of both neutral and charged Mn doped B cluster \\text{MnB}nQ (n  =  10-20 and Q  =  0, ±1) have been proposed through extensive first-principles swarm-intelligence based structure searches. It is found that Mn doping has significantly modified the grow behaviors of B clusters, leading to two novel structural transitions from planar to tubular and then to cage-like B structures in both neutral and charged species. Half-sandwich-type structures are most favorable for small \\text{MnB}n-/0/+ (n  ⩽  13) clusters and gradually transform to Mn-centered double-ring tubular structures at \\text{MnB}16-/0/+ clusters with superior thermodynamic stabilities compared with their neighbors. Most strikingly, endohedral cages become the ground-state structures for larger \\text{MnB}n-/0/+ (n  ⩾  19) clusters, among which \\text{MnB}20+ adopts a highly symmetric structure with superior thermodynamic stability and a large HOMO-LUMO gap of 4.53 eV. The unique stability of the endohedral \\text{MnB}\\text{20}+ cage is attributed to the geometric fit and formation of 18-electron closed-shell configuration. The results significantly advance our understanding about the structure and bonding of B-based clusters and strongly suggest transition-metal doping as a viable route to synthesize intriguing B-based nanomaterials.

Vapor deposition of water on graphitic surfaces: formation of amorphous ice, bilayer ice, ice I, and liquid water.

PubMed

Lupi, Laura; Kastelowitz, Noah; Molinero, Valeria

2014-11-14

Carbonaceous surfaces are a major source of atmospheric particles and could play an important role in the formation of ice. Here we investigate through molecular simulations the stability, metastability, and molecular pathways of deposition of amorphous ice, bilayer ice, and ice I from water vapor on graphitic and atomless Lennard-Jones surfaces as a function of temperature. We find that bilayer ice is the most stable ice polymorph for small cluster sizes, nevertheless it can grow metastable well above its region of thermodynamic stability. In agreement with experiments, the simulations predict that on increasing temperature the outcome of water deposition is amorphous ice, bilayer ice, ice I, and liquid water. The deposition nucleation of bilayer ice and ice I is preceded by the formation of small liquid clusters, which have two wetting states: bilayer pancake-like (wetting) at small cluster size and droplet-like (non-wetting) at larger cluster size. The wetting state of liquid clusters determines which ice polymorph is nucleated: bilayer ice nucleates from wetting bilayer liquid clusters and ice I from non-wetting liquid clusters. The maximum temperature for nucleation of bilayer ice on flat surfaces, T(B)(max) is given by the maximum temperature for which liquid water clusters reach the equilibrium melting line of bilayer ice as wetting bilayer clusters. Increasing water-surface attraction stabilizes the pancake-like wetting state of liquid clusters leading to larger T(B)(max) for the flat non-hydrogen bonding surfaces of this study. The findings of this study should be of relevance for the understanding of ice formation by deposition mode on carbonaceous atmospheric particles, including soot.

A Comparison of Heuristic Procedures for Minimum within-Cluster Sums of Squares Partitioning

ERIC Educational Resources Information Center

Brusco, Michael J.; Steinley, Douglas

2007-01-01

Perhaps the most common criterion for partitioning a data set is the minimization of the within-cluster sums of squared deviation from cluster centroids. Although optimal solution procedures for within-cluster sums of squares (WCSS) partitioning are computationally feasible for small data sets, heuristic procedures are required for most practical…

Insights into genetic diversity and biological propensities of potentially zoonotic avian influenza H9N2 viruses circulating in Egypt.

PubMed

Naguib, Mahmoud M; Arafa, Abdel-Satar; Parvin, Rokshana; Beer, Martin; Vahlenkamp, Thomas; Harder, Timm C

2017-11-01

Low pathogenic avian influenza (LPAI) H9N2 viruses have established endemic status in Egyptian poultry populations since 2012. Recently, four cases of human H9N2 virus infections in Egypt demonstrated the zoonotic potential of these viruses. Egyptian H9N2 viruses obtained from 2011 to 2014 phylogenetically grouped into three clusters (1-3) within subclade B of the G1 lineage. Antigenically, a close clustering of the Egyptian H9N2 viruses with other recent G1-B like H9N2 strains and a significant antigenic distance from viruses outside the G1-B lineage was evident. Recent Egyptian LPAIV H9N2 showed a tendency to increased binding with erythrocytes expressing α 2,6-linked sialic acid which correlated with the Q226L amino acid substitution at the receptor binding unit of the hemagglutinin (Q234L, H9 numbering). Sequence analyses of the N2 neuraminidase (NA) revealed substitutions in the NA hemadsorption site similar to the N2 of prepandemic H3N2/1968, but no distinct antigenic or functional characteristics of the H9N2 NA associated with increased zoonotic potential could be identified. Copyright © 2017 Elsevier Inc. All rights reserved.

Infrared Spectra of M^+(2-AMINO-1-PHENYL ETHANOL)(H_2O)_{n=0-2}Ar (M=Na, K)

NASA Astrophysics Data System (ADS)

Nicely, Amy L.; Lisy, James M.

2009-06-01

A balance of competing electrostatic and hydrogen bonding interactions directs the structure of hydrated gas-phase cluster ions. Because of this, a biologically relevant model of cluster structures should include the effects of surrounding water molecules and metal ions such as sodium and potassium, which are found in high concentrations in the bloodstream. The molecule 2-amino-1-phenyl ethanol (APE) serves as a model for the neurotransmitters ephedrine and adrenaline. The neutral APE molecule contains an internal hydrogen bond between the amino and hydroxyl groups. In the M^+(APE) complex, the cation can either interrupt the internal hydrogen bond or position itself above the phenyl group, leaving the internal hydrogen bond intact. The former is preferred based on DFT calculations (B3LYP/6-31+G*) for both K^+ and Na^+ across the entire range from 0-400K, but infrared photodissociation (IRPD) spectra indicate a preference for the latter configuration at low temperatures. The IRPD spectra of M^+(H_2O)_{n=1-2} and M^+(H_2O)_{n=0-2}Ar (M=Na, K) will be presented along with parallel DFT and thermodynamics calculations to assist with the identification of the isomers present in each experiment.

Why do gallium clusters have a higher melting point than the bulk?

PubMed

Chacko, S; Joshi, Kavita; Kanhere, D G; Blundell, S A

2004-04-02

Density functional molecular dynamical simulations have been performed on Ga17 and Ga13 clusters to understand the recently observed higher-than-bulk melting temperatures in small gallium clusters [Phys. Rev. Lett. 91, 215508 (2003)

Irradiation-induced microchemical changes in highly irradiated 316 stainless steel

NASA Astrophysics Data System (ADS)

Fujii, K.; Fukuya, K.

2016-02-01

Cold-worked 316 stainless steel specimens irradiated to 74 dpa in a pressurized water reactor (PWR) were analyzed by atom probe tomography (APT) to extend knowledge of solute clusters and segregation at higher doses. The analyses confirmed that those clusters mainly enriched in Ni-Si or Ni-Si-Mn were formed at high number density. The clusters were divided into three types based on their size and Mn content; small Ni-Si clusters (3-4 nm in diameter), and large Ni-Si and Ni-Si-Mn clusters (8-10 nm in diameter). The total cluster number density was 7.7 × 1023 m-3. The fraction of large clusters was almost 1/10 of the total density. The average composition (in at%) for small clusters was: Fe, 54; Cr, 12; Mn, 1; Ni, 22; Si, 11; Mo, 1, and for large clusters it was: Fe, 44; Cr, 9; Mn, 2; Ni, 29; Si, 14; Mo,1. It was likely that some of the Ni-Si clusters correspond to γ‧ phase precipitates while the Ni-Si-Mn clusters were precursors of G phase precipitates. The APT analyses at grain boundaries confirmed enrichment of Ni, Si, P and Cu and depletion of Fe, Cr, Mo and Mn. The segregation behavior was consistent with previous knowledge of radiation induced segregation.

Synthesis and first use of pyridine-2,6-diylbis(pyrazine-2-ylmethanone) in metal cluster chemistry: a {Mn(III)3Na2} complex with an ideal trigonal bipyramidal geometry.

PubMed

Giannopoulos, Dimosthenis P; Wilson-Konderka, Cody; Gagnon, Kevin J; Teat, Simon J; Escuer, Albert; Metallinos, Costa; Stamatatos, Theocharis C

2015-03-07

The successful organic synthesis of a new dipyrazole/pyridine-dicarbonyl organic molecule, namely pyridine-2,6-diylbis(pyrazine-2-ylmethanone) [(pz)CO(py)CO(pz)], followed by its employment in Mn coordination chemistry has yielded the neutral cluster compound [Mn3Na2O(N3)3(L)3] (1), where L(2-) is the (pz)C(CH2COCH3)(O(-))(py)C(CH2COCH3)(O(-))(pz) dianion. The latter group was formed in situ, presumably by the nucleophilic attack of the carbanion (-)CH2COCH3 to the carbonyl carbon atoms of (pz)CO(py)CO(pz), in the presence of Mn(n+) ions under basic conditions and in solvent Me2CO. Complex 1 possesses an almost ideal trigonal bipyramidal topology, with the two Na(I) ions occupying the apical positions and the three Mn(III) ions residing in the equatorial trigonal plane. The bridging ligation about the metal ions is provided by a μ3-O(2-) ion and six μ-OR(-) groups from the L(2-) ligand, while peripheral ligation is completed by three terminal azido groups and the pyridine N and carbonyl O atoms of L(2-). Magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions between the paramagnetic Mn(III) centres; the use of an anisotropic, equilateral Mn(III)3 triangle model allowed us to fit the magnetic data and obtain the best-fit parameters: J = -10.8 cm(-1), D = -5.3 cm(-1), and g = 1.99. The combined results demonstrate the rich chemical reactivity of carbonyl groups and the ability of poly-ketone ligands to stabilize cluster compounds with unprecedented structural motifs and interesting architectures.

Microbiomes structure and diversity in different horizons of full soil profiles

NASA Astrophysics Data System (ADS)

Chernov, Timofey; Tkhakakhova, Azida; Zhelezova, Alena; Semenov, Mikhail; Kutovaya, Olga

2017-04-01

Topsoil is a most common object for soil metagenomic studies; sometimes soil profile is being formally split in layers by depth. However, Russian Soil Science School formulated the idea of soil profile as a complex of soil horizons, which can differ in their properties and genesis. In this research we analyzed 57 genetic soil horizons of 8 different soils from European part of Russia: Albeluvisol, Greyzemic Phaeozem, three Chermozems (different land use - till, fallow, wind-protecting tree line), Rhodic Cambisol, Haplic Kastanozem and Salic Solonetz (WRB classification). Sampling was performed from all genetic horizons in each soil profile starting from topsoil until subsoil. Total DNA was extracted and 16S rRNA sequencing was provided together with chemical analysis of soil (pH measurement, C and N contents, etc.). Structure and diversity of prokaryotic community are significantly different in those soil horizons, which chemical properties and processes of origin are contrasting with nearest horizons: Na-enriched horizon of Solonetz, eluvial horizon of Albeluvisol, plough pan of Agrochernozem. Actinobacteria were abundant in top horizons of soils in warm and dry climate, while Acidobacteria had the highest frequency in soils of moist and cold regions. Concerning Archaea, Thaumarchaeota prevailed in all studied soils. Their rate was higher in microbiomes of upper horizons of steppe soils and it was reducing with depth down the profile. Prokaryotic communities in Chernozems were clustered by soil horizons types: microbiomes of A (organic topsoil) and B (mineral) horizons formed non-overlapping clusters by principal component analysis, cluster formed by prokaryotic communities of transitional soil horizons (AB) take place between clusters of A and B horizons. Moreover, prokaryotic communities of A horizons differ from each other strongly, while microbiomes of B horizons formed a narrow small cluster. It must be explaned by more diverse conditions in upper A horizons. Thus, ecological differences between soil horizons are important factor of differentiation of prokaryotic communities in soil profile; their structure can be specific for horizon type. This study was supported by Russian Science Foundation, project no. 14-26-00079

Exploring supervised and unsupervised methods to detect topics in biomedical text

PubMed Central

Lee, Minsuk; Wang, Weiqing; Yu, Hong

2006-01-01

Background Topic detection is a task that automatically identifies topics (e.g., "biochemistry" and "protein structure") in scientific articles based on information content. Topic detection will benefit many other natural language processing tasks including information retrieval, text summarization and question answering; and is a necessary step towards the building of an information system that provides an efficient way for biologists to seek information from an ocean of literature. Results We have explored the methods of Topic Spotting, a task of text categorization that applies the supervised machine-learning technique naïve Bayes to assign automatically a document into one or more predefined topics; and Topic Clustering, which apply unsupervised hierarchical clustering algorithms to aggregate documents into clusters such that each cluster represents a topic. We have applied our methods to detect topics of more than fifteen thousand of articles that represent over sixteen thousand entries in the Online Mendelian Inheritance in Man (OMIM) database. We have explored bag of words as the features. Additionally, we have explored semantic features; namely, the Medical Subject Headings (MeSH) that are assigned to the MEDLINE records, and the Unified Medical Language System (UMLS) semantic types that correspond to the MeSH terms, in addition to bag of words, to facilitate the tasks of topic detection. Our results indicate that incorporating the MeSH terms and the UMLS semantic types as additional features enhances the performance of topic detection and the naïve Bayes has the highest accuracy, 66.4%, for predicting the topic of an OMIM article as one of the total twenty-five topics. Conclusion Our results indicate that the supervised topic spotting methods outperformed the unsupervised topic clustering; on the other hand, the unsupervised topic clustering methods have the advantages of being robust and applicable in real world settings. PMID:16539745

Integrated K-band spectra of old and intermediate-age globular clusters in the Large Magellanic Cloud

NASA Astrophysics Data System (ADS)

Lyubenova, M.; Kuntschner, H.; Rejkuba, M.; Silva, D. R.; Kissler-Patig, M.; Tacconi-Garman, L. E.; Larsen, S. S.

2010-02-01

Current stellar population models have arguably the largest uncertainties in the near-IR wavelength range, partly due to a lack of large and well calibrated empirical spectral libraries. In this paper we present a project whose aim it is to provide the first library of luminosity weighted integrated near-IR spectra of globular clusters to be used to test the current stellar population models and serve as calibrators for future ones. Our pilot study presents spatially integrated K-band spectra of three old (≥10 Gyr) and metal poor ([Fe/H] ~ -1.4), and three intermediate age (1-2 Gyr) and more metal rich ([Fe/H] ~ - 0.4) globular clusters in the LMC. We measured the line strengths of the Na I, Ca I and 12CO (2-0) absorption features. The Na I index decreases with increasing age and decreasing metallicity of the clusters. The DCO index, used to measure the 12CO (2-0) line strength, is significantly reduced by the presence of carbon-rich TP-AGB stars in the globular clusters with age ~1 Gyr. This is in contradiction to the predictions of the stellar population models of Maraston (2005, MNRAS, 362, 799). We find that this disagreement is due to the different CO absorption strength of carbon-rich Milky Way TP-AGB stars used in the models and the LMC carbon stars in our sample. For globular clusters with age ≥ 2 Gyr we find DCO index measurements consistent with the model predictions. Based on observation collected at the ESO Paranal La Silla Observatory, Chile, Prog. ID 078.B-0205.Spectra in FITS format are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/510/A19

Development of small scale cluster computer for numerical analysis

NASA Astrophysics Data System (ADS)

Zulkifli, N. H. N.; Sapit, A.; Mohammed, A. N.

2017-09-01

In this study, two units of personal computer were successfully networked together to form a small scale cluster. Each of the processor involved are multicore processor which has four cores in it, thus made this cluster to have eight processors. Here, the cluster incorporate Ubuntu 14.04 LINUX environment with MPI implementation (MPICH2). Two main tests were conducted in order to test the cluster, which is communication test and performance test. The communication test was done to make sure that the computers are able to pass the required information without any problem and were done by using simple MPI Hello Program where the program written in C language. Additional, performance test was also done to prove that this cluster calculation performance is much better than single CPU computer. In this performance test, four tests were done by running the same code by using single node, 2 processors, 4 processors, and 8 processors. The result shows that with additional processors, the time required to solve the problem decrease. Time required for the calculation shorten to half when we double the processors. To conclude, we successfully develop a small scale cluster computer using common hardware which capable of higher computing power when compare to single CPU processor, and this can be beneficial for research that require high computing power especially numerical analysis such as finite element analysis, computational fluid dynamics, and computational physics analysis.

Effect of a small amount of sodium carbonate on konjac glucomannan-induced changes in wheat starch gel.

PubMed

Zhou, Yun; Zhao, Dan; Winkworth-Smith, Charles G; Foster, Tim J; Nirasawa, Satoru; Tatsumi, Eizo; Cheng, Yongqiang

2015-02-13

Wheat starch gels were produced with konjac glucomannan (KGM) and low concentrations of Na2CO3 (0.1-0.2 wt% of starch) using a rapid viscosity analyzer (RVA). The gelling properties of wheat starch in varying ratios of KGM and Na2CO3 were characterized by differential scanning calorimetry (DSC), rheometry and confocal laser scanning microscopy (CLSM). A small amount of Na2CO3 resulted in gels with increased elasticity whereas structural ordering during retrogradation was insignificantly affected. Comparison of CLSM images of composite gels revealed that Na2CO3 at 0.2 wt% of starch allowed the formation of fiber-like extensions around scattered swollen granules by KGM and amylose interaction, making swollen granules disperse within the micro phase, which was not typical in CLSM images of gels in the absence of Na2CO3. Dynamic storage modulus and dynamic power law exponent were substantially higher than those observed for the same concentration of KGM in the presence of Na2CO3, supporting the hypothesis that Na2CO3 could promote strong interchain associations between KGM and starch components. Copyright © 2014 Elsevier Ltd. All rights reserved.

Electronic structures and thermochemical properties of the small silicon-doped boron clusters B(n)Si (n=1-7) and their anions.

PubMed

Tai, Truong Ba; Kadłubański, Paweł; Roszak, Szczepan; Majumdar, Devashis; Leszczynski, Jerzy; Nguyen, Minh Tho

2011-11-18

We perform a systematic investigation on small silicon-doped boron clusters B(n)Si (n=1-7) in both neutral and anionic states using density functional (DFT) and coupled-cluster (CCSD(T)) theories. The global minima of these B(n)Si(0/-) clusters are characterized together with their growth mechanisms. The planar structures are dominant for small B(n)Si clusters with n≤5. The B(6)Si molecule represents a geometrical transition with a quasi-planar geometry, and the first 3D global minimum is found for the B(7)Si cluster. The small neutral B(n)Si clusters can be formed by substituting the single boron atom of B(n+1) by silicon. The Si atom prefers the external position of the skeleton and tends to form bonds with its two neighboring B atoms. The larger B(7)Si cluster is constructed by doping Si-atoms on the symmetry axis of the B(n) host, which leads to the bonding of the silicon to the ring boron atoms through a number of hyper-coordination. Calculations of the thermochemical properties of B(n)Si(0/-) clusters, such as binding energies (BE), heats of formation at 0 K (ΔH(f)(0)) and 298 K (ΔH(f)([298])), adiabatic (ADE) and vertical (VDE) detachment energies, and dissociation energies (D(e)), are performed using the high accuracy G4 and complete basis-set extrapolation (CCSD(T)/CBS) approaches. The differences of heats of formation (at 0 K) between the G4 and CBS approaches for the B(n)Si clusters vary in the range of 0.0-4.6 kcal mol(-1). The largest difference between two approaches for ADE values is 0.15 eV. Our theoretical predictions also indicate that the species B(2)Si, B(4)Si, B(3)Si(-) and B(7)Si(-) are systems with enhanced stability, exhibiting each a double (σ and π) aromaticity. B(5)Si(-) and B(6)Si are doubly antiaromatic (σ and π) with lower stability. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Polaronic and ionic conduction in NaMnO2: influence of native point defects

NASA Astrophysics Data System (ADS)

Zhu, Zhen; Peelaers, Hartwin; van de Walle, Chris G.

Layered NaMnO2 has promising applications as a cathode material for sodium ion batteries. We will discuss strategies to improve the electrical performance of NaMnO2, including how to optimize the conditions of synthesis and how impurity doping affects the performance. Using hybrid density functional theory, we explored the structural, electronic, and defect properties of bulk NaMnO2. It is antiferromagnetic in the ground state with a band gap of 3.75 eV. Small hole and electron polarons can form in the bulk either through self-trapping or adjacent to point defects. We find that both Na and Mn vacancies are shallow acceptors with the induced holes trapped as small polarons, while O vacancies are deep defect centers. Cation antisites, especially MnNa, are found to have low formation energies. As a result, we expect that MnNa exists in as-grown NaMnO2 in moderate concentrations, rather than forming only at a later stage of the charging process, at which point it causes undesirable structural phase transitions. Both electronic conduction, via polaron hopping, and ionic conduction, through VNa migration, are significantly affected by the presence of point defects. This work was supported by DOE.

Salt-induced aggregation and fusion of dioctadecyldimethylammonium chloride and sodium dihexadecylphosphate vesicles.

PubMed Central

Carmona-Ribeiro, A M; Chaimovich, H

1986-01-01

Small dioctadecyldimethylammonium chloride (DODAC) vesicles prepared by sonication fuse upon addition of NaCl as detected by several methods (electron microscopy, trapped volume determinations, temperature-dependent phase transition curves, and osmometer behavior. In contrast, small sodium dihexadecyl phosphate (DHP) vesicles mainly aggregate upon NaCl addition as shown by electron microscopy and the lack of osmometer behavior. Scatter-derived absorbance changes of small and large DODAC or DHP vesicles as a function of time after salt addition were obtained for a range of NaCl or amphiphile concentration. These changes were interpreted in accordance with a phenomenological model based upon fundamental light-scattering laws and simple geometrical considerations. Short-range hydration repulsion between DODAC (or DHP) vesicles is possibly the main energy barrier for the fusion process. Images FIGURE 2 FIGURE 9 PMID:3779002

Subaru Weak-Lensing Survey II: Multi-Object Spectroscopy and Cluster Masses

NASA Astrophysics Data System (ADS)

Hamana, Takashi; Miyazaki, Satoshi; Kashikawa, Nobunari; Ellis, Richard S.; Massey, Richard J.; Refregier, Alexandre; Taylor, James E.

2009-08-01

We present the first results of a multi-object spectroscopic campaign to follow up cluster candidates located via weak lensing. Our main goals are to search for spatial concentrations of galaxies that are plausible optical counterparts of the weak-lensing signals, and to determine the cluster redshifts from those of member galaxies. Around each of 36 targeted cluster candidates, we obtained 15-32 galaxy redshifts. For 28 of these targets, we confirmed a secure cluster identification, with more than five spectroscopic galaxies within a velocity of ±3000km s-1. This includes three cases where two clusters at different redshifts are projected along the same line-of-sight. In 6 of the 8 unconfirmed targets, we found multiple small galaxy concentrations at different redshifts, each containing at least three spectroscopic galaxies. The weak-lensing signal around those systems was thus probably created by the projection of groups or small clusters along the same line-of-sight. In both of the remaining two targets, a single small galaxy concentration was found. In some candidate super-cluster systems, we found additional evidence of filaments connecting the main density peak to an additional nearby structure. For a subsample of our most cleanly measured clusters, we investigated the statistical relation between their weak-lensing mass (MNFW, σSIS) and the velocity dispersion of their member galaxies (σv), comparing our sample with optically and X-ray selected samples from the literature. Our lensing-selected clusters are consistent with σv = σSIS, with a similar scatter to that of optically and X-ray selected clusters. We also derived an empirical relation between the cluster mass and the galaxy velocity dispersion, M200E(z) = 11.0 × 1014 × (σv/1000km s-1)3.0 h-1 Modot, which is in reasonable agreement with predictions of N-body simulations in the Λ CDM cosmology.

Age determination of 15 old to intermediate-age small Magellanic cloud star clusters

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

Parisi, M. C.; Clariá, J. J.; Piatti, A. E.

2014-04-01

We present color-magnitude diagrams in the V and I bands for 15 star clusters in the Small Magellanic Cloud (SMC) based on data taken with the Very Large Telescope (VLT, Chile). We selected these clusters from our previous work, wherein we derived cluster radial velocities and metallicities from calcium II infrared triplet (CaT) spectra also taken with the VLT. We discovered that the ages of six of our clusters have been appreciably underestimated by previous studies, which used comparatively small telescopes, graphically illustrating the need for large apertures to obtain reliable ages of old and intermediate-age SMC star clusters. Inmore » particular, three of these clusters, L4, L6, and L110, turn out to be among the oldest SMC clusters known, with ages of 7.9 ± 1.1, 8.7 ± 1.2, and 7.6 ± 1.0 Gyr, respectively, helping to fill a possible 'SMC cluster age gap'. Using the current ages and metallicities from Parisi et al., we analyze the age distribution, age gradient, and age-metallicity relation (AMR) of a sample of SMC clusters measured homogeneously. There is a suggestion of bimodality in the age distribution but it does not show a constant slope for the first 4 Gyr, and we find no evidence for an age gradient. Due to the improved ages of our cluster sample, we find that our AMR is now better represented in the intermediate/old period than we had derived in Parisi et al., where we simply took ages available in the literature. Additionally, clusters younger than ∼4 Gyr now show better agreement with the bursting model of Pagel and Tautvaišienė, but we confirm that this model is not a good representation of the AMR during the intermediate/old period. A more complicated model is needed to explain the SMC chemical evolution in that period.« less

Infrared predissociation spectroscopy of M+ (C6H6)(1-4)(H2O)(1-2)Ar(0-1) cluster ions, M = Li, Na.

PubMed

Beck, Jordan P; Lisy, James M

2011-05-05

Infrared predissociation (IRPD) spectra of Li(+)(C(6)H(6))(1-4)(H(2)O)(1-2)Ar(0-1) and Na(+)(C(6)H(6))(2-4)(H(2)O)(1-2)Ar(1) are presented along with ab initio calculations. The results indicate that the global minimum energy structure for Li(+)(C(6)H(6))(2)(H(2)O)(2) has each water forming a π-hydrogen bond with the same benzene molecule. This bonding motif is preserved in Li(+)(C(6)H(6))(3-4)(H(2)O)(2)Ar(0-1) with the additional benzene ligands binding to the available free OH groups. Argon tagging allows high-energy Li(+)(C(6)H(6))(2-4)(H(2)O)(2)Ar isomers containing water-water hydrogen bonds to be trapped and detected. The monohydrated, Li(+) containing clusters contain benzene-water interactions with varying strength as indicated by shifts in OH stretching frequencies. The IRPD spectra of M(+)(C(6)H(6))(1-4)(H(2)O)(1-2)Ar are very different for lithium-bearing versus sodium-bearing cluster ions emphasizing the important role of ion size in determining the most favorable balance of competing noncovalent interactions.

Probing the Initial Mass Function in Extended Ultraviolet (XUV) Disks

NASA Astrophysics Data System (ADS)

Koda, Jin

2012-01-01

"The GALEX UV satellite discovered tantalizing evidence of star formation (SF) far beyond the optical edge of galactic disks (i.e. extended UV disk, or XUV disk). This discovery provides a new opportunity for studying SF in the exceedingly low-density environment (˜1/10 of typical SF density), spurring intense debate on the universality of the initial mass function (IMF) in such exceptional environments. Our pilot S-Cam study of M83’s XUV disk led to support for the universal IMF at least in M83 (Koda et al. 2012). We propose an expansion of the pilot study, observing 6 XUV disks in NA656(Hα), B, I, and R-band with S-Cam. In conjunction with GALEX UV bands, these images will reveal the presence of O stars (Hα; NA656-R) and O&B stars (UV) in stellar clusters -thus, constraining the high-mass end of the IMF. The multi-broadband images will enable us to determine the masses of the clusters with much improved accuracy (previously, relied only on R). The proposed observations will not only increase the statistical significance of our previous result, but also enable us to analyze the stochastic effect of IMF sampling in very low-mass clusters (10^{2+3} M_sun) - the regime about which there is much ongoing debate."

Shield fields: Concentrations of small volcanic edifices on Venus

NASA Technical Reports Server (NTRS)

Aubele, J. C.; Crumpler, L. S.

1992-01-01

Pre-Magellan analysis of the Venera 15/16 data indicated the existence of abundant small volcanic edifices, each less than or equal to 20 km diameter, interpreted to be predominantly shield volcanoes and occurring throughout the plains terrain, most common in equidimensional clusters. With the analysis of Magellan data, these clusters of greater than average concentration of small volcanic edifices have been called 'shield fields'. Although individual small shields can and do occur almost everywhere on the plains terrain of Venus, they most commonly occur in fields that are well-defined, predominantly equant, clusters of edifices. Major questions include why the edifices are concentrated in this way, how they relate to the source of the eruptive material, and what the possible relationship of shield fields to plains terrain is. There are three possible models for the origin of fields and small shields: (1) a field represents an 'island' of higher topography subsequently surrounded by later plains material; and (2) a field represents the area of magma reservoir.

Hydrogen bonding interaction of small acetaldehyde clusters studied with core-electron excitation spectroscopy in the oxygen K-edge region

NASA Astrophysics Data System (ADS)

Tabayashi, K.; Chohda, M.; Yamanaka, T.; Tsutsumi, Y.; Takahashi, O.; Yoshida, H.; Taniguchi, M.

2010-06-01

In order to examine inner-shell electron excitation spectra of molecular clusters with strong multipole interactions, excitation spectra and time-of-flight (TOF) fragment-mass spectra of small acetaldehyde (AA) clusters have been studied under the beam conditions. The TOF spectra at the oxygen K-edge region showed an intense growth of the protonated clusters, MnH+ (M=CH3CHO) in the cluster beams. "cluster-specific" excitation spectra could be generated by monitoring partial-ion-yields of the protonated clusters. The most intense band of O1s→π*CO was found to shift to a higher energy by 0.15 eV relative to the monomer band upon clusterization. X-ray absorption spectra (XAS) were also calculated for the representative dimer configurations using a computer modelling program based on the density functional theory. The XAS prediction for the most stable (non-planar) configuration was found to give a close comparison with the cluster-band shift observed. The band shift was interpreted as being due to the HOMO-LUMO interaction within the complex where a contribution of vibrationally blue-shifting hydrogen bonding could be identified.

Ab initio calculations of optical properties of silver clusters: cross-over from molecular to nanoscale behavior

NASA Astrophysics Data System (ADS)

Titantah, John T.; Karttunen, Mikko

2016-05-01

Electronic and optical properties of silver clusters were calculated using two different ab initio approaches: (1) based on all-electron full-potential linearized-augmented plane-wave method and (2) local basis function pseudopotential approach. Agreement is found between the two methods for small and intermediate sized clusters for which the former method is limited due to its all-electron formulation. The latter, due to non-periodic boundary conditions, is the more natural approach to simulate small clusters. The effect of cluster size is then explored using the local basis function approach. We find that as the cluster size increases, the electronic structure undergoes a transition from molecular behavior to nanoparticle behavior at a cluster size of 140 atoms (diameter ~1.7 nm). Above this cluster size the step-like electronic structure, evident as several features in the imaginary part of the polarizability of all clusters smaller than Ag147, gives way to a dominant plasmon peak localized at wavelengths 350 nm ≤ λ ≤ 600 nm. It is, thus, at this length-scale that the conduction electrons' collective oscillations that are responsible for plasmonic resonances begin to dominate the opto-electronic properties of silver nanoclusters.

The Relationship of Sodium and Oxygen in Galactic Field RR Lyrae Stars

NASA Astrophysics Data System (ADS)

Andrievsky, S.; Wallerstein, G.; Korotin, S.; Lyashko, D.; Kovtyukh, V.; Tsymbal, V.; Davis, C. E.; Gomez, T.; Huang, W.; Farrell, E. M.

2018-02-01

We analyzed 62 high-resolution spectra of 30 Galactic Field RR Lyrae-type stars with the aim of deriving their atmospheric parameters (T eff , {log}g, V t ), metallicity ([Fe/H]), radial velocities, and NLTE abundances of oxygen and sodium. We found that there is no clear anti-correlation between [O/Fe] and [Na/Fe] as is seen in globular clusters. On this basis, we conclude that the majority of field RR Lyrae-type stars should hardly be considered to be remnants of the dissolution of globular clusters.

Mitochondrial filaments and clusters as intracellular power-transmitting cables.

PubMed

Skulachev, V P

2001-01-01

Mitochondria exist in two interconverting forms; as small isolated particles, and as extended filaments, networks or clusters connected with intermitochondrial junctions. Extended mitochondria can represent electrically united systems, which can facilitate energy delivery from the cell periphery to the cell core and organize antioxidant defence of the cell interior when O2 is consumed by mitochondrial clusters near the the outer cell membrane, and protonic potential is transmitted to the cell core mitochondria to form ATP. As to small mitochondria, they might represent a transportable form of these organelles.

Pico-level DNA sensing by hetero-polymetalate, Na10{Dy2W10O30(µ-S)6}·80H2O, cluster

NASA Astrophysics Data System (ADS)

Dutta, Taposhree; Ganguly, Jhuma; Sarkar, Sabyasachi

2018-04-01

The polyoxometalate dysprosium cluster, (Dy-S-W POM) , Na10[Dy2W10O30(µ-S)6]·80H2O, shows remarkable dsDNA denaturation property. In the presence of 0.22 µmol of this Dy-S-W POM, the melting temperature (Tm) of calf-thymus (CT) dsDNA is decreased to 62.35 °C. Dy-S-W POM shows bleaching of methylene blue (MB). Addition of CT-DNA in the MB bleached solution of Dy-S-W POM apparently intercalates MB. Such trapped MB by CT-DNA responds to its re-oxidation by elemental sulfur formed in the bleaching process involving Dy-S-W POM. This reduction-oxidation property of MB with Dy-S-W POM led to the detection of pico (13.20 pmol) level of DNA even by naked eye, which will be helpful for rapid trace DNA detection in forensic science and DNA-related diagnostics, complimenting time-consuming sophisticated methodology.

Comparisons of fish species traits from small streams to large rivers

USGS Publications Warehouse

Goldstein, R.M.; Meador, M.R.

2004-01-01

To examine the relations between fish community function and stream size, we classified 429 lotic freshwater fish species based on multiple categories within six species traits: (1) substrate preference, (2) geomorphic preference, (3) trophic ecology, (4) locomotion morphology, (5) reproductive strategy, and (6) stream size preference. Stream size categories included small streams, small, medium, and large rivers, and no size preference. The frequencies of each species trait category were determined for each stream size category based on life history information from the literature. Cluster analysis revealed the presence of covarying groups of species trait categories. One cluster (RUN) included the traits of planktivore and herbivore feeding ecology, migratory reproductive behavior and broadcast spawning, preferences for main-channel habitats, and a lack of preferences for substrate type. The frequencies of classifications for the RUN cluster varied significantly across stream size categories (P = 0.009), being greater for large rivers than for small streams and rivers. Another cluster (RIFFLE) included the traits of invertivore feeding ecology, simple nester reproductive behavior, a preference for riffles, and a preference for bedrock, boulder, and cobble-rubble substrate. No significant differences in the frequency of classifications among stream size categories were detected for the RIFFLE cluster (P = 0.328). Our results suggest that fish community function is structured by large-scale differences in habitat and is different for large rivers than for small streams and rivers. Our findings support theoretical predictions of variation in species traits among stream reaches based on ecological frameworks such as landscape filters, habitat templates, and the river continuum concept. We believe that the species trait classifications presented here provide an opportunity for further examination of fish species' relations to physical, chemical, and biological factors in lotic habitats ranging from small streams to large rivers.

Predicting the points of interaction of small molecules in the NF-κB pathway

PubMed Central

2011-01-01

Background The similarity property principle has been used extensively in drug discovery to identify small compounds that interact with specific drug targets. Here we show it can be applied to identify the interactions of small molecules within the NF-κB signalling pathway. Results Clusters that contain compounds with a predominant interaction within the pathway were created, which were then used to predict the interaction of compounds not included in the clustering analysis. Conclusions The technique successfully predicted the points of interactions of compounds that are known to interact with the NF-κB pathway. The method was also shown to be successful when compounds for which the interaction points were unknown were included in the clustering analysis. PMID:21342508

Cluster-specific small airway modeling for imaging-based CFD analysis of pulmonary air flow and particle deposition in COPD smokers

NASA Astrophysics Data System (ADS)

Haghighi, Babak; Choi, Jiwoong; Choi, Sanghun; Hoffman, Eric A.; Lin, Ching-Long

2017-11-01

Accurate modeling of small airway diameters in patients with chronic obstructive pulmonary disease (COPD) is a crucial step toward patient-specific CFD simulations of regional airflow and particle transport. We proposed to use computed tomography (CT) imaging-based cluster membership to identify structural characteristics of airways in each cluster and use them to develop cluster-specific airway diameter models. We analyzed 284 COPD smokers with airflow limitation, and 69 healthy controls. We used multiscale imaging-based cluster analysis (MICA) to classify smokers into 4 clusters. With representative cluster patients and healthy controls, we performed multiple regressions to quantify variation of airway diameters by generation as well as by cluster. The cluster 2 and 4 showed more diameter decrease as generation increases than other clusters. The cluster 4 had more rapid decreases of airway diameters in the upper lobes, while cluster 2 in the lower lobes. We then used these regression models to estimate airway diameters in CT unresolved regions to obtain pressure-volume hysteresis curves using a 1D resistance model. These 1D flow solutions can be used to provide the patient-specific boundary conditions for 3D CFD simulations in COPD patients. Support for this study was provided, in part, by NIH Grants U01-HL114494, R01-HL112986 and S10-RR022421.

Kinetics of aggregation in charged nanoparticle solutions driven by different mechanisms

NASA Astrophysics Data System (ADS)

Abbas, S.; Yadav, I.; Kumar, Sugam; Aswal, V. K.; Kohlbrecher, J.

2017-05-01

The structure and kinetics during aggregation of anionic silica nanoparticles as induced through different mechanisms have been studied by dynamic light scattering (DLS) and small-angle neutron scattering (SANS). Three different additives, namely an electrolyte (NaCl), cationic protein (lysozyme) and non-ionic surfactant (C12E10) were used to initiate nanoparticle aggregation. Electrolyte induced aggregation can be explained by DLVO interaction, whereas depletion interaction (non-DLVO interaction) is found responsible for nanoparticle aggregation in case of non-ionic surfactant. Unlike these two cases, strong electrostatic attraction between nanoparticle and oppositely charged protein results into protein-mediated nanoparticle aggregation. The electrolyte induced aggregation show quite slow aggregation rate whereas protein mediated as well as surfactant induced aggregation takes place almost instantaneously. The significant differences observed in the kinetics are explained based on range of interactions responsible for the aggregation. In spite of differences in mechanism and kinetics, the nanoparticle clusters are found to have similar fractal morphology (fractal dimension ˜ 2.5) in all the three cases.

Application of Scan Statistics to Detect Suicide Clusters in Australia

PubMed Central

Cheung, Yee Tak Derek; Spittal, Matthew J.; Williamson, Michelle Kate; Tung, Sui Jay; Pirkis, Jane

2013-01-01

Background Suicide clustering occurs when multiple suicide incidents take place in a small area or/and within a short period of time. In spite of the multi-national research attention and particular efforts in preparing guidelines for tackling suicide clusters, the broader picture of epidemiology of suicide clustering remains unclear. This study aimed to develop techniques in using scan statistics to detect clusters, with the detection of suicide clusters in Australia as example. Methods and Findings Scan statistics was applied to detect clusters among suicides occurring between 2004 and 2008. Manipulation of parameter settings and change of area for scan statistics were performed to remedy shortcomings in existing methods. In total, 243 suicides out of 10,176 (2.4%) were identified as belonging to 15 suicide clusters. These clusters were mainly located in the Northern Territory, the northern part of Western Australia, and the northern part of Queensland. Among the 15 clusters, 4 (26.7%) were detected by both national and state cluster detections, 8 (53.3%) were only detected by the state cluster detection, and 3 (20%) were only detected by the national cluster detection. Conclusions These findings illustrate that the majority of spatial-temporal clusters of suicide were located in the inland northern areas, with socio-economic deprivation and higher proportions of indigenous people. Discrepancies between national and state/territory cluster detection by scan statistics were due to the contrast of the underlying suicide rates across states/territories. Performing both small-area and large-area analyses, and applying multiple parameter settings may yield the maximum benefits for exploring clusters. PMID:23342098

Stressful jobs and non-stressful jobs: a cluster analysis of office jobs.

PubMed

Carayon, P

1994-02-01

The purpose of the study was to determine if office jobs could be characterized by a small number of combinations of stressors that could be related to job-title information and self-report of psychological strain. Two-hundred-and-sixty-two office workers from three public service organizations provided data on nine job stressors and seven indicators of psychological strain. Using cluster analysis on the nine stressors, office jobs were classified into three clusters. The first cluster included jobs with high skill utilization, task clarity, job control and social support and low future ambiguity, but also high on job demands such as quantitative work-load, attention and work pressure. The second cluster included jobs with high demands and future ambiguity and low skill utilization, task clarity, job control and social support. The third cluster was intermediary between the first two clusters. The three clusters were related to job-title information. The second cluster was the highest on a range of psychological strain indicators, while the other two clusters were high on certain strain indicators but low on others. The study showed that office jobs could be characterized by a small number of combinations of stressors that were related to job-title information and psychological strain.

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

NASA Astrophysics Data System (ADS)

Piatti, A. E.

2018-07-01

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

High performance electrolytes for MCFC

DOEpatents

Kaun, Thomas D.; Roche, Michael F.

1999-01-01

A carbonate electrolyte of the Li/Na or CaBaLiNa system. The Li/Na carbonate has a composition displaced from the eutectic composition to diminish segregation effects in a molten carbonate fuel cell. The CaBaLiNa system includes relatively small amounts of Ca.sub.2 CO.sub.3 and BaCO.sub.3, and preferably of equimolar amounts. The presence of both Ca and BaCO.sub.3 enables lower temperature fuel cell operation.

Theoretical realization of cluster-assembled hydrogen storage materials based on terminated carbon atomic chains.

PubMed

Liu, Chun-Sheng; An, Hui; Guo, Ling-Ju; Zeng, Zhi; Ju, Xin

2011-01-14

The capacity of carbon atomic chains with different terminations for hydrogen storage is studied using first-principles density functional theory calculations. Unlike the physisorption of H(2) on the H-terminated chain, we show that two Li (Na) atoms each capping one end of the odd- or even-numbered carbon chain can hold ten H(2) molecules with optimal binding energies for room temperature storage. The hybridization of the Li 2p states with the H(2)σ orbitals contributes to the H(2) adsorption. However, the binding mechanism of the H(2) molecules on Na arises only from the polarization interaction between the charged Na atom and the H(2). Interestingly, additional H(2) molecules can be bound to the carbon atoms at the chain ends due to the charge transfer between Li 2s2p (Na 3s) and C 2p states. More importantly, dimerization of these isolated metal-capped chains does not affect the hydrogen binding energy significantly. In addition, a single chain can be stabilized effectively by the C(60) fullerenes termination. With a hydrogen uptake of ∼10 wt.% on Li-coated C(60)-C(n)-C(60) (n = 5, 8), the Li(12)C(60)-C(n)-Li(12)C(60) complex, keeping the number of adsorbed H(2) molecules per Li and stabilizing the dispersion of individual Li atoms, can serve as better building blocks of polymers than the (Li(12)C(60))(2) dimer. These findings suggest a new route to design cluster-assembled hydrogen storage materials based on terminated sp carbon chains.

Simultaneous ion and neutral evaporation in aqueous nanodrops: experiment, theory, and molecular dynamics simulations.

PubMed

Higashi, Hidenori; Tokumi, Takuya; Hogan, Christopher J; Suda, Hiroshi; Seto, Takafumi; Otani, Yoshio

2015-06-28

We use a combination of tandem ion mobility spectrometry (IMS-IMS, with differential mobility analyzers), molecular dynamics (MD) simulations, and analytical models to examine both neutral solvent (H2O) and ion (solvated Na(+)) evaporation from aqueous sodium chloride nanodrops. For experiments, nanodrops were produced via electrospray ionization (ESI) of an aqueous sodium chloride solution. Two nanodrops were examined in MD simulations: a 2500 water molecule nanodrop with 68 Na(+) and 60 Cl(-) ions (an initial net charge of z = +8), and (2) a 1000 water molecule nanodrop with 65 Na(+) and 60 Cl(-) ions (an initial net charge of z = +5). Specifically, we used MD simulations to examine the validity of a model for the neutral evaporation rate incorporating both the Kelvin (surface curvature) and Thomson (electrostatic) influences, while both MD simulations and experimental measurements were compared to predictions of the ion evaporation rate equation of Labowsky et al. [Anal. Chim. Acta, 2000, 406, 105-118]. Within a single fit parameter, we find excellent agreement between simulated and modeled neutral evaporation rates for nanodrops with solute volume fractions below 0.30. Similarly, MD simulation inferred ion evaporation rates are in excellent agreement with predictions based on the Labowsky et al. equation. Measurements of the sizes and charge states of ESI generated NaCl clusters suggest that the charge states of these clusters are governed by ion evaporation, however, ion evaporation appears to have occurred with lower activation energies in experiments than was anticipated based on analytical calculations as well as MD simulations. Several possible reasons for this discrepancy are discussed.

The possible crossover effects of NaNO3 confined in porous media: From bulk to clusters

NASA Astrophysics Data System (ADS)

Mu, R.; Jin, F.; Morgan, S. H.; Henderson, D. O.; Silberman, E.

1994-05-01

Differential scanning calorimetry (DSC) and Raman spectra are reported for NaNO3 bulk and for NaNO3 confined in porous silica with pore radii, rp=2.5, 5, 10, 20 nm. Raman spectra are also given for a 6 M solution of NaNO3. The melting transition for the confined NaNO3 exhibits a 1/rp dependence where rp is the pore radius for rp≳5 nm. No melting transition is observed for NaNO3 confined in 2.5 nm pores. Above this pore size, their appears to be a deviation in the melting transition dependence on rp. The internal modes observed in the Raman spectra for the confined material are in agreement with those of the bulk solid except for a feature observed on the low frequency side of the ν1 band. The external TO mode observed at 100 cm-1 and the librational mode at 175 cm-1 for NaNO3 both decrease in intensity and broaden as rp decreases and both bands disappear at rp=2.5 nm. An additional peak at 70 cm-1 not observed in the solution or bulk NaNO3 spectra appears in the spectra of confined NaNO3 and increases in intensity as rp decreases. We assign this band to a new phase of NaNO3 which is stabilized by the surface hydroxyl groups of the porous silica. For NaNO3 confined in pores, rp≤2.5 nm, we suggest that NaNO3 exists as disordered aggregates.

Direct demonstration of persistent Na+ channel activity in dendritic processes of mammalian cortical neurones

PubMed Central

Magistretti, Jacopo; Ragsdale, David S; Alonso, Angel

1999-01-01

Single Na+ channel activity was recorded in patch-clamp, cell-attached experiments performed on dendritic processes of acutely isolated principal neurones from rat entorhinal-cortex layer II. The distances of the recording sites from the soma ranged from ≈20 to ≈100 μm.Step depolarisations from holding potentials of −120 to −100 mV to test potentials of −60 to +10 mV elicited Na+ channel openings in all of the recorded patches (n= 16).In 10 patches, besides transient Na+ channel openings clustered within the first few milliseconds of the depolarising pulses, prolonged and/or late Na+ channel openings were also regularly observed. This ‘persistent’ Na+ channel activity produced net inward, persistent currents in ensemble-average traces, and remained stable over the entire duration of the experiments (≈9 to 30 min).Two of these patches contained <= 3 channels. In these cases, persistent Na+ channel openings could be attributed to the activity of one single channel.The voltage dependence of persistent-current amplitude in ensemble-average traces closely resembled that of whole-cell, persistent Na+ current expressed by the same neurones, and displayed the same characteristic low threshold of activation.Dendritic, persistent Na+ channel openings had relatively high single-channel conductance (≈20 pS), similar to what is observed for somatic, persistent Na+ channels.We conclude that a stable, persistent Na+ channel activity is expressed by proximal dendrites of entorhinal-cortex layer II principal neurones, and can contribute a significant low-threshold, persistent Na+ current to the dendritic processing of excitatory synaptic inputs. PMID:10601494

Tracing the Chemical Evolution of Metal-rich Galactic Bulge Globular Clusters

NASA Astrophysics Data System (ADS)

Munoz Gonzalez, Cesar; Saviane, Ivo; Geisler, Doug; Villanova, Sandro

2018-01-01

We present in this poster the metallicity characterization of the four metal rich Bulge Galactic Gobular Clusters, which have controversial metallicities. We analyzed our high-resolution spectra (using UVES-580nm and GIRAFFE-HR13 setups) for a large sample of RGB/AGB targets in each cluster in order to measure their metallicity and prove or discard the iron spread hypothesis. We have also characterized chemically stars with potentially different iron content by measuring light (O, Na, Mg, Al), alpha (Si, Ca, Ti), iron–peak (V, Cr, Ni, Mn) and s and r process (Y, Zr, Ba, Eu) elements. We have identified possible channels responsible for the chemical heterogeneity of the cluster populations, like AGB or massive fast-rotating stars contamination, or SN explosion. Also, we have analyzed the origin and evolution of these bulge GCs and their connection with the bulge itself.

Reduced expression of Na(v)1.6 sodium channels and compensation by Na(v)1.2 channels in mice heterozygous for a null mutation in Scn8a.

PubMed

Vega, Ana V; Henry, Diane L; Matthews, Gary

2008-09-05

The voltage-gated sodium channel alpha subunit Na(v)1.6, encoded by the Scn8a gene, accumulates at high density at mature nodes of Ranvier of myelinated axons, replacing the Na(v)1.2 channels found at nodes earlier in development. To investigate this preferential expression of Na(v)1.6 at adult nodes, we examined isoform-specific expression of sodium channels in mice heterozygous for a null mutation in Scn8a. Immunoblots from these +/- mice had 50% of the wild-type level of Na(v)1.6 protein, and their optic-nerve nodes of Ranvier had correspondingly less anti-Na(v)1.6 immunofluorescence. Protein level and nodal immunofluorescence of the Na(v)1.2 alpha subunit increased in Scn8a(+/-) mice, keeping total sodium channel expression approximately constant despite partial loss of Na(v)1.6 channels. The results are consistent with a model in which Na(v)1.6 and Na(v)1.2 compete for binding partners at sites of high channel density, such as nodes of Ranvier. We suggest that Na(v)1.6 channels normally occupy most of the molecular machinery responsible for channel clustering because they have higher binding affinity, and not because they are exclusively recognized by mechanisms for transport and insertion of sodium channels in myelinated axons. The reduced amount of Na(v)1.6 protein in Scn8a(+/-) mice is apparently insufficient to saturate the nodal binding sites, allowing Na(v)1.2 channels to compete more successfully.

Galaxy And Mass Assembly (GAMA): the signatures of galaxy interactions as viewed from small scale galaxy clustering

NASA Astrophysics Data System (ADS)

Gunawardhana, M. L. P.; Norberg, P.; Zehavi, I.; Farrow, D. J.; Loveday, J.; Hopkins, A. M.; Davies, L. J. M.; Wang, L.; Alpaslan, M.; Bland-Hawthorn, J.; Brough, S.; Holwerda, B. W.; Owers, M. S.; Wright, A. H.

2018-06-01

Statistical studies of galaxy-galaxy interactions often utilise net change in physical properties of progenitors as a function of the separation between their nuclei to trace both the strength and the observable timescale of their interaction. In this study, we use two-point auto, cross and mark correlation functions to investigate the extent to which small-scale clustering properties of star forming galaxies can be used to gain physical insight into galaxy-galaxy interactions between galaxies of similar optical brightness and stellar mass. The Hα star formers, drawn from the highly spatially complete Galaxy And Mass Assembly (GAMA) survey, show an increase in clustering on small separations. Moreover, the clustering strength shows a strong dependence on optical brightness and stellar mass, where (1) the clustering amplitude of optically brighter galaxies at a given separation is larger than that of optically fainter systems, (2) the small scale clustering properties (e.g. the strength, the scale at which the signal relative to the fiducial power law plateaus) of star forming galaxies appear to differ as a function of increasing optical brightness of galaxies. According to cross and mark correlation analyses, the former result is largely driven by the increased dust content in optically bright star forming galaxies. The latter could be interpreted as evidence of a correlation between interaction-scale and optical brightness of galaxies, where physical evidence of interactions between optically bright star formers, likely hosted within relatively massive halos, persist over larger separations than those between optically faint star formers.

Theoretical study of the electronic and optical properties of photochromic dithienylethene derivatives connected to small gold clusters.

PubMed

Perrier, Aurélie; Maurel, François; Aubard, Jean

2007-10-04

In the course of developing electronic devices on a molecular scale, dithienylethenes photochromic molecules constitute promising candidates for optoelectronic applications such as memories and switches. There is thus a great interest to understand and control the switching behavior of photochromic compounds deposited on metallic surfaces or nanoparticles. Within the framework of the density functional theory, we studied the effect of small gold clusters (Au3 and Au9) on the electronic structure and absorption spectrum of a model dithienylethene molecule. The molecular orbital interactions between the photochromic molecule and the gold cluster made it possible to rationalize some experimental findings (Dulic, D.; van der Molen, S. J.; Kudernac, T.; Jonkman, H. T.; de Jong, J. J. D.; Bowden, T. N.; van Esch, J.; Feringa, B. L.; van Wees, B. J. Phys. Rev. Lett. 2003, 91, 207402). For the closed-ring isomer, grafting a photochromic molecule on a small gold cluster does not change the characteristics of the electronic transition involved in the ring-opening reaction. On the opposite, the absorption spectrum of the photochromic open-ring isomer is strongly modified by the inclusion of the metallic cluster. In agreement with experimental results, our study thus showed that the cycloreversion reaction which involves the closed-ring isomer should be still possible, whereas the ring-closure reaction which involves the open-ring isomer should be inhibited. Connecting a dithienylethene molecule to a small gold cluster hence provides a qualitative comprehension of the photochromic activities of dithienylethenes connected to a gold surface.

Unexpected Actinyl Cation-Directed Structural Variation in Neptunyl(VI) A-Type Tri-lacunary Heteropolyoxotungstate Complexes

DOE PAGES

Berg, John M.; Gaunt, Andrew J.; May, Iain; ...

2015-04-22

A-type tri-lacunary heteropolyoxotungstate anions (e.g., [PW 9O 34] 9-, [AsW 9O 34] 9-, [SiW 9O 34] 10- and [GeW 9O 34] 10-) are multi-dentate oxygen donor ligands that readily form sandwich complexes with actinyl cations ({UO 2} 2+, {NpO 2} +, {NpO 2} 2+ & {PuO 2} 2+) in near neutral/slightly alkaline aqueous solutions. Two or three actinyl cations are sandwiched between two trilacunary anions, with additional cations (Na +, K + or NH 4 +) also often held within the cluster. Studies thus far have indicated that it is these additional +I cations, rather than the specific actinylmore » cation, that direct the structural variation in the complexes formed. We now report the structural characterization of the neptunyl (VI) cluster complex (NH 4) 13 [Na(NpO 2) 2(A-α- PW 9O 34) 2]·12H 2O. The anion in this complex, [Na(NpO 2) 2(PW 9O 34) 2] 13-, contains one Na + cation and two {NpO 2} 2+ cations held between two [PW 9O 34] 9- anions – with an additional partial occupancy NH 4 + or {NpO 2} 2+ cation also present. In the analogous uranium (VI) system, under similar reaction conditions that includes an excess of NH 4Cl in the parent solution, it was previously shown that [(NH 4) 2(U VIO 2) 2(A-PW 9O 34) 2] 12- is the dominant species in both solution and the crystallized salt. Spectroscopic studies provide further proof of differences in the observed chemistry for the {NpO 2} 2+/[PW 9O 34] 9- and {UO 2} 2+/[PW 9O 34] 9- systems, both in solution and in solid state complexes crystallized from comparable salt solutions. The work revealed that varying the actinide element (Np vs. U) can indeed measurably impact structure and complex stability in the cluster chemistry of actinyl (VI) cations with A-type tri-lacunary heteropolyoxotungstate anions.« less

Derivatized gold clusters and antibody-gold cluster conjugates

DOEpatents

Hainfeld, James F.; Furuya, Frederic R.

1994-11-01

Antibody- or antibody fragment-gold cluster conjugates are shown wherein the conjugate size can be as small as 5.0 nm. Methods and reagents are disclosed in which antibodies, Fab' or F(ab').sub.2 fragments thereof are covalently bound to a stable cluster of gold atoms. The gold clusters may contain 6, 8, 9, 11, 13, 55 or 67 gold atoms in their inner core. The clusters may also contain radioactive gold. The antibody-cluster conjugates are useful in electron microscopy applications as well as in clinical applications that include imaging, diagnosis and therapy.

Star-like superalkali cations featuring planar pentacoordinate carbon

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

Guo, Jin-Chang; Tian, Wen-Juan; Zhao, Xue-Feng

Superalkali cations, known to possess low vertical electron affinities (VEAs), high vertical detachment energies, and large highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gaps, are intriguing chemical species. Thermodynamically, such species need to be the global minima in order to serve as the promising targets for experimental realization. In this work, we propose the strategies of polyhalogenation and polyalkalination for designing the superalkali cations. By applying these strategies, the local-minimum planar pentacoordinate carbon (ppC) cluster CBe{sub 5} can be modified to form a series of star-like superalkali ppC or quasi-ppC CBe{sub 5}X{sub 5}{sup +} (X = F,more » Cl, Br, Li, Na, K) cations containing a CBe{sub 5} moiety. Polyhalogenation and polyalkalination on the CBe{sub 5} unit may help eliminate the high reactivity of bare CBe{sub 5} molecule by covering the reactive Be atoms with noble halogen anions and alkali cations. Computational exploration of the potential energy surfaces reveals that the star-like ppC or quasi-ppC CBe{sub 5}X{sub 5}{sup +} (X = F, Cl, Br, Li, Na, K) clusters are the true global minima of the systems. The predicted VEAs for CBe{sub 5}X{sub 5}{sup +} range from 3.01 to 3.71 eV for X = F, Cl, Br and 2.12–2.51 eV for X = Li, Na, K, being below the lower bound of the atomic ionization potential of 3.89 eV in the periodic table. Large HOMO-LUMO energy gaps are also revealed for the species: 10.76–11.07 eV for X = F, Cl, Br and 4.99–6.91 eV for X = Li, Na, K. These designer clusters represent the first series of superalkali cations with a ppC center. Bonding analyses show five Be–X–Be three-center two-electron (3c-2e) σ bonds for the peripheral bonding, whereas the central C atom is associated with one 6c-2e π bond and three 6c-2e σ bonds, rendering (π and σ) double aromaticity. Born-Oppenheimer molecular dynamics simulations indicate that the CBe{sub 5} motif is robust in the clusters. As planar hypercoordination carbon species are often thermodynamically unstable and highly reactive, the superalkali cation characters of these ppC species should be highlighted, which may be suitable for experimental realization.« less

Performance of small cluster surveys and the clustered LQAS design to estimate local-level vaccination coverage in Mali.

PubMed

Minetti, Andrea; Riera-Montes, Margarita; Nackers, Fabienne; Roederer, Thomas; Koudika, Marie Hortense; Sekkenes, Johanne; Taconet, Aurore; Fermon, Florence; Touré, Albouhary; Grais, Rebecca F; Checchi, Francesco

2012-10-12

Estimation of vaccination coverage at the local level is essential to identify communities that may require additional support. Cluster surveys can be used in resource-poor settings, when population figures are inaccurate. To be feasible, cluster samples need to be small, without losing robustness of results. The clustered LQAS (CLQAS) approach has been proposed as an alternative, as smaller sample sizes are required. We explored (i) the efficiency of cluster surveys of decreasing sample size through bootstrapping analysis and (ii) the performance of CLQAS under three alternative sampling plans to classify local VC, using data from a survey carried out in Mali after mass vaccination against meningococcal meningitis group A. VC estimates provided by a 10 × 15 cluster survey design were reasonably robust. We used them to classify health areas in three categories and guide mop-up activities: i) health areas not requiring supplemental activities; ii) health areas requiring additional vaccination; iii) health areas requiring further evaluation. As sample size decreased (from 10 × 15 to 10 × 3), standard error of VC and ICC estimates were increasingly unstable. Results of CLQAS simulations were not accurate for most health areas, with an overall risk of misclassification greater than 0.25 in one health area out of three. It was greater than 0.50 in one health area out of two under two of the three sampling plans. Small sample cluster surveys (10 × 15) are acceptably robust for classification of VC at local level. We do not recommend the CLQAS method as currently formulated for evaluating vaccination programmes.

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 .

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

Sun, Shengtong; Chevrier, Daniel M.; Zhang, Peng

Amorphous intermediate phases are vital precursors in the crystallization of many biogenic minerals. While inherent short-range orders have been found in amorphous calcium carbonates (ACCs) relating to different crystalline forms, it has never been clarified experimentally whether such orders already exist in very small clusters less than 2 nm in size. Here, we studied the stability and structure of 10,12-pentacosadiynoic acid (PCDA) protected ACC clusters with a core size of ca. 1.4 nm consisting of only seven CaCO 3 units. Ligand concentration and structure are shown to be key factors in stabilizing the ACC clusters. More importantly, even in suchmore » small CaCO 3 entities, a proto-calcite short-range order can be identified but with a relatively high degree of disorder that arises from the very small size of the CaCO 3 core. Our findings support the notion of a structural link between prenucleation clusters, amorphous intermediates, and final crystalline polymorphs, which appears central to the understanding of polymorph selection.« less

Characteristics of voxel prediction power in full-brain Granger causality analysis of fMRI data

NASA Astrophysics Data System (ADS)

Garg, Rahul; Cecchi, Guillermo A.; Rao, A. Ravishankar

2011-03-01

Functional neuroimaging research is moving from the study of "activations" to the study of "interactions" among brain regions. Granger causality analysis provides a powerful technique to model spatio-temporal interactions among brain regions. We apply this technique to full-brain fMRI data without aggregating any voxel data into regions of interest (ROIs). We circumvent the problem of dimensionality using sparse regression from machine learning. On a simple finger-tapping experiment we found that (1) a small number of voxels in the brain have very high prediction power, explaining the future time course of other voxels in the brain; (2) these voxels occur in small sized clusters (of size 1-4 voxels) distributed throughout the brain; (3) albeit small, these clusters overlap with most of the clusters identified with the non-temporal General Linear Model (GLM); and (4) the method identifies clusters which, while not determined by the task and not detectable by GLM, still influence brain activity.

VizieR Online Data Catalog: Shape parameters for 154 Galactic open clusters (Zhai+, 2017)

NASA Astrophysics Data System (ADS)

Zhai, M.; Abt, H.; Zhao, G.; Li, C.

2017-06-01

The data used are from database WEBDA (http://www.univie.ac.at/webda/). We have found 946 open clusters with equatorial coordinates for each cluster member. Since cluster members are easily contaminated by field stars, we have only adopted stars with membership probabilities higher than 70% as cluster members. It is rarely possible to determine a cluster's shape with a small number of members, so we have only considered relatively richer clusters, which host more than 20 of the most probable member stars. After these selections, there are 154 clusters left. (1 data file).

A two-step non-flowcytometry-based naïve B cell isolation method and its application in Staphylococcal enterotoxin B (SEB) presentation.

PubMed

Chokeshai-u-saha, Kaj; Buranapraditkun, Supranee; Jacquet, Alain; Nguyen, Catherine; Ruxrungtham, Kiat

2012-09-01

To study the role of human naïve B cells in antigen presentation and stimulation to naïve CD4+ T cell, a suitable method to reproducibly isolate sufficient naïve B cells is required. To improve the purity of isolated naive B cells obtained from a conventional one-step magnetic bead method, we added a rosetting step to enrich total B cell isolates from human whole blood samples prior to negative cell sorting by magnetic beads. The acquired naïve B cells were analyzed for phenotypes and for their role in Staphylococcal enterotoxin B (SEB) presentation to naïve CD4+ T cells. The mean (SD) naïve B cell (CD19+/CD27-) purity obtained from this two-step method compared with the one-step method was 97% (1.0) versus 90% (1.2), respectively. This two-step method can be used with a sample of whole blood as small as 10 ml. The isolated naive B cells were phenotypically at a resting state and were able to prime naïve CD4+ T cell activation by Staphylococcal enterotoxin B (SEB) presentation. This two-step non-flow cytometry-based approach improved the purity of isolated naïve B cells compared with conventional one-step magnetic bead method. It also worked well with a small blood volume. In addition, this study showed that the isolated naïve B cells can present a super-antigen "SEB" to activate naïve CD4 cells. These methods may thus be useful for further in vitro characterization of human naïve B cells and their roles as antigen presenting cells in various diseases.

Vacancy clustering and acceptor activation in nitrogen-implanted ZnO

NASA Astrophysics Data System (ADS)

Børseth, Thomas Moe; Tuomisto, Filip; Christensen, Jens S.; Monakhov, Edouard V.; Svensson, Bengt G.; Kuznetsov, Andrej Yu.

2008-01-01

The role of vacancy clustering and acceptor activation on resistivity evolution in N ion-implanted n -type hydrothermally grown bulk ZnO has been investigated by positron annihilation spectroscopy, resistivity measurements, and chemical profiling. Room temperature 220keV N implantation using doses in the low 1015cm-2 range induces small and big vacancy clusters containing at least 2 and 3-4 Zn vacancies, respectively. The small clusters are present already in as-implanted samples and remain stable up to 1000°C with no significant effect on the resistivity evolution. In contrast, formation of the big clusters at 600°C is associated with a significant increase in the free electron concentration attributed to gettering of amphoteric Li impurities by these clusters. Further annealing at 800°C results in a dramatic decrease in the free electron concentration correlated with activation of 1016-1017cm-3 acceptors likely to be N and/or Li related. The samples remain n type, however, and further annealing at 1000°C results in passivation of the acceptor states while the big clusters dissociate.

Symmetries and stability of chimera states in small, globally-coupled networks

NASA Astrophysics Data System (ADS)

Hart, Joseph D.; Bansal, Kanika; Murphy, Thomas E.; Roy, Rajarshi

It has recently been demonstrated that symmetries in a network's topology can help predict the patterns of synchronized clusters that can emerge in a network of coupled oscillators. This and related discoveries have led to increased interest in both network symmetries and cluster synchronization. In parallel with these discoveries, interest in chimera states-dynamical patterns in which a network separates into coherent and incoherent portions-has grown, and chimeras have now been observed in a variety of experimental systems. We present an opto-electronic experiment in which both chimera states and synchronized clusters are observed in a small, globally-coupled network. We show that the symmetries and sub-symmetries of the network permit the formation of the chimera and cluster states. A recently developed group theoretical approach enables us to predict the stability of the observed chimera and cluster states, and highlights the close relationship between chimera and cluster states as belonging to the broader phenomenon of partial synchronization.

Size dependent fragmentation of argon clusters in the soft x-ray ionization regime

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

Gisselbrecht, Mathieu; Lindgren, Andreas; Burmeister, Florian

Photofragmentation of argon clusters of average size ranging from 10 up to 1000 atoms is studied using soft x-ray radiation below the 2p threshold and multicoincidence mass spectroscopy technique. For small clusters (=10), ionization induces fast fragmentation with neutral emission imparting a large amount of energy. While the primary dissociation takes place on a picosecond time scale, the fragments undergo slow degradation in the spectrometer on a microsecond time scale. For larger clusters ({>=}100) we believe that we observe the fragmentation pattern of multiply charged species on a time-scale which lasts a few hundred nanoseconds. The reason for these slowermore » processes is the large number of neutral atoms which act as an efficient cooling bath where the excess energy ('heat') dissipates among all degrees of freedom. Further degradation of the photoionic cluster in spectrometer then takes place on the microsecond time scale, similar to small clusters.« less

Polymorphism in magic-sized Au144(SR)60 clusters

NASA Astrophysics Data System (ADS)

Jensen, Kirsten M. Ø.; Juhas, Pavol; Tofanelli, Marcus A.; Heinecke, Christine L.; Vaughan, Gavin; Ackerson, Christopher J.; Billinge, Simon J. L.

2016-06-01

Ultra-small, magic-sized metal nanoclusters represent an important new class of materials with properties between molecules and particles. However, their small size challenges the conventional methods for structure characterization. Here we present the structure of ultra-stable Au144(SR)60 magic-sized nanoclusters obtained from atomic pair distribution function analysis of X-ray powder diffraction data. The study reveals structural polymorphism in these archetypal nanoclusters. In addition to confirming the theoretically predicted icosahedral-cored cluster, we also find samples with a truncated decahedral core structure, with some samples exhibiting a coexistence of both cluster structures. Although the clusters are monodisperse in size, structural diversity is apparent. The discovery of polymorphism may open up a new dimension in nanoscale engineering.

Cooperative network clustering and task allocation for heterogeneous small satellite network

NASA Astrophysics Data System (ADS)

Qin, Jing

The research of small satellite has emerged as a hot topic in recent years because of its economical prospects and convenience in launching and design. Due to the size and energy constraints of small satellites, forming a small satellite network(SSN) in which all the satellites cooperate with each other to finish tasks is an efficient and effective way to utilize them. In this dissertation, I designed and evaluated a weight based dominating set clustering algorithm, which efficiently organizes the satellites into stable clusters. The traditional clustering algorithms of large monolithic satellite networks, such as formation flying and satellite swarm, are often limited on automatic formation of clusters. Therefore, a novel Distributed Weight based Dominating Set(DWDS) clustering algorithm is designed to address the clustering problems in the stochastically deployed SSNs. Considering the unique features of small satellites, this algorithm is able to form the clusters efficiently and stably. In this algorithm, satellites are separated into different groups according to their spatial characteristics. A minimum dominating set is chosen as the candidate cluster head set based on their weights, which is a weighted combination of residual energy and connection degree. Then the cluster heads admit new neighbors that accept their invitations into the cluster, until the maximum cluster size is reached. Evaluated by the simulation results, in a SSN with 200 to 800 nodes, the algorithm is able to efficiently cluster more than 90% of nodes in 3 seconds. The Deadline Based Resource Balancing (DBRB) task allocation algorithm is designed for efficient task allocations in heterogeneous LEO small satellite networks. In the task allocation process, the dispatcher needs to consider the deadlines of the tasks as well as the residue energy of different resources for best energy utilization. We assume the tasks adopt a Map-Reduce framework, in which a task can consist of multiple subtasks. The DBRB algorithm is deployed on the head node of a cluster. It gathers the status from each cluster member and calculates their Node Importance Factors (NIFs) from the carried resources, residue power and compute capacity. The algorithm calculates the number of concurrent subtasks based on the deadlines, and allocates the subtasks to the nodes according to their NIF values. The simulation results show that when cluster members carry multiple resources, resource are more balanced and rare resources serve longer in DBRB than in the Earliest Deadline First algorithm. We also show that the algorithm performs well in service isolation by serving multiple tasks with different deadlines. Moreover, the average task response time with various cluster size settings is well controlled within deadlines as well. Except non-realtime tasks, small satellites may execute realtime tasks as well. The location-dependent tasks, such as image capturing, data transmission and remote sensing tasks are realtime tasks that are required to be started / finished on specific time. The resource energy balancing algorithm for realtime and non-realtime mixed workload is developed to efficiently schedule the tasks for best system performance. It calculates the residue energy for each resource type and tries to preserve resources and node availability when distributing tasks. Non-realtime tasks can be preempted by realtime tasks to provide better QoS to realtime tasks. I compared the performance of proposed algorithm with a random-priority scheduling algorithm, with only realtime tasks, non-realtime tasks and mixed tasks. It shows the resource energy reservation algorithm outperforms the latter one with both balanced and imbalanced workloads. Although the resource energy balancing task allocation algorithm for mixed workload provides preemption mechanism for realtime tasks, realtime tasks can still fail due to resource exhaustion. For LEO small satellite flies around the earth on stable orbits, the location-dependent realtime tasks can be considered as periodical tasks. Therefore, it is possible to reserve energy for these realtime tasks. The resource energy reservation algorithm preserves energy for the realtime tasks when the execution routine of periodical realtime tasks is known. In order to reserve energy for tasks starting very early in each period that the node does not have enough energy charged, an energy wrapping mechanism is also designed to calculate the residue energy from the previous period. The simulation results show that without energy reservation, realtime task failure rate can reach more than 60% when the workload is highly imbalanced. In contrast, the resource energy reservation produces zero RT task failures and leads to equal or better aggregate system throughput than the non-reservation algorithm. The proposed algorithm also preserves more energy because it avoids task preemption. (Abstract shortened by ProQuest.).

The Cluster Environment of Two High-mass Protostars

NASA Astrophysics Data System (ADS)

Montes, Virginie; Hofner, Peter

2017-06-01

Characterizing the environment and stellar population in which high-mass stars form is an important step to decide between the main massive star formation theories. In the monolithic collapse model, the mass of the core will determine the final stellar mass (e.g., McKee & Tan 2003). In contrast, in the competitive accretion model (e.g., Bonnell & Bate 2006), the mass of the high-mass star is related to the properties of the cluster. As dynamical processes substantially affect the appearance of a cluster, we study early stages of high-mass star formation. These regions often show extended emission from hot dust at infrared wavelengths, which can cause difficulties to define the cluster. We use a multi-wavelength technique to study nearby high-mass star clusters, based on X-ray observations with the Chandra X-Ray Telescope, in conjunction with infrared data and VLA data. The technique relies on the fact that YSOs are particularly bright in X-ray and that contamination is relatively small. X-ray observations allow us to determine the cluster size. The cluster membership and YSOs classification is established using infrared identification of the X-ray sources, and color-color and color-magnitude diagrams.In this talk, I will present our findings on the cluster study of two high-mass star forming regions: IRAS 20126+4104 and IRAS 16562-3959. While most massive stars appear to be formed in rich a cluster environment, those two sources are candidates for the formation of massive stars in a relatively poor cluster. In contrast to what was found in previous studies (Qiu et al. 2008), the dominant B0-type protostar in IRAS 20126+4104 is associated with a small cluster of low-mass stars. I will also show our current work on IRAS 16562-3959, which contains one of the most luminous O-type protostars in the Galaxy. In the vicinity of this particularly interesting region there is a multitude of small clusters, for which I will present how their stellar population differ from the high-mass star-forming cluster IRAS 16562-3959.

Species collapse via hybridization in Darwin's tree finches.

PubMed

Kleindorfer, Sonia; O'Connor, Jody A; Dudaniec, Rachael Y; Myers, Steven A; Robertson, Jeremy; Sulloway, Frank J

2014-03-01

Species hybridization can lead to fitness costs, species collapse, and novel evolutionary trajectories in changing environments. Hybridization is predicted to be more common when environmental conditions change rapidly. Here, we test patterns of hybridization in three sympatric tree finch species (small tree finch Camarhynchus parvulus, medium tree finch Camarhynchus pauper, and large tree finch: Camarhynchus psittacula) that are currently recognized on Floreana Island, Galápagos Archipelago. Genetic analysis of microsatellite data from contemporary samples showed two genetic populations and one hybrid cluster in both 2005 and 2010; hybrid individuals were derived from genetic population 1 (small morph) and genetic population 2 (large morph). Females of the large and rare species were more likely to pair with males of the small common species. Finch populations differed in morphology in 1852-1906 compared with 2005/2010. An unsupervised clustering method showed (a) support for three morphological clusters in the historical tree finch sample (1852-1906), which is consistent with current species recognition; (b) support for two or three morphological clusters in 2005 with some (19%) hybridization; and (c) support for just two morphological clusters in 2010 with frequent (41%) hybridization. We discuss these findings in relation to species demarcations of Camarhynchus tree finches on Floreana Island.

First principles investigations of small bimetallic PdGa clusters as catalysts for hydrogen dissociation

NASA Astrophysics Data System (ADS)

Kaul, Indu; Ghosh, Prasenjit

2017-04-01

Using first principles density functional theory based calculations, we have studied hydrogen dissociation on sub nanometer bimetallic clusters formed from d-block (Pd) and p-block (Ga) elements in gas phase to explore the feasibility of using them as cheap catalysts for hydrogen dissociation. Our calculations show that the dimers, trimers and tetramers of these clusters are thermodynamically more stable than the pure ones for all Ga concentrations. For a given cluster size, we find that the clusters containing equal amount of Pd and Ga are the most stable ones. In contrast to bulk PdGa, the contribution of Pd-d states to the highest occupied molecular orbitals of the bimetallic clusters are either very small or absent. Study of adsorption of hydrogen molecule on these clusters show that hydrogen binds in an activated form only on the Pd rich clusters. From the calculations of hydrogen dissociation barriers on tetramers of pure Pd, 25% Ga (Pd3Ga) and 50% Ga (Pd2Ga2) we find that Pd3Ga is the most efficient catalyst for hydrogen dissociation with barriers even lower than that on the PdGa surfaces.

Observation of small cluster formation in concentrated monoclonal antibody solutions and its implications to solution viscosity.

PubMed

Yearley, Eric J; Godfrin, Paul D; Perevozchikova, Tatiana; Zhang, Hailiang; Falus, Peter; Porcar, Lionel; Nagao, Michihiro; Curtis, Joseph E; Gawande, Pradad; Taing, Rosalynn; Zarraga, Isidro E; Wagner, Norman J; Liu, Yun

2014-04-15

Monoclonal antibodies (mAbs) are a major class of biopharmaceuticals. It is hypothesized that some concentrated mAb solutions exhibit formation of a solution phase consisting of reversibly self-associated aggregates (or reversible clusters), which is speculated to be responsible for their distinct solution properties. Here, we report direct observation of reversible clusters in concentrated solutions of mAbs using neutron spin echo. Specifically, a stable mAb solution is studied across a transition from dispersed monomers in dilute solution to clustered states at more concentrated conditions, where clusters of a preferred size are observed. Once mAb clusters have formed, their size, in contrast to that observed in typical globular protein solutions, is observed to remain nearly constant over a wide range of concentrations. Our results not only conclusively establish a clear relationship between the undesirable high viscosity of some mAb solutions and the formation of reversible clusters with extended open structures, but also directly observe self-assembled mAb protein clusters of preferred small finite size similar to that in micelle formation that dominate the properties of concentrated mAb solutions. Copyright © 2014 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Selective synthesis of FAU-type zeolites

NASA Astrophysics Data System (ADS)

Garcia, Gustavo; Cabrera, Saúl; Hedlund, Jonas; Mouzon, Johanne

2018-05-01

In the present work, parameters influencing the selectivity of the synthesis of FAU-zeolites from diatomite were studied. The final products after varying synthesis time were characterized by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction and gas adsorption. It was found that high concentrations of NaCl could completely inhibit the formation of zeolite P, which otherwise usually forms as soon as maximum FAU crystallinity is reached. In the presence of NaCl, the FAU crystals were stable for extended time after completed crystallization of FAU before formation of sodalite. It was also found that addition of NaCl barely changed the crystallization kinetics of FAU zeolite and only reduced the final FAU particle size and SiO2/Al2O3 ratio slightly. Other salts containing either Na or Cl were also investigated. Our results suggest that there is a synergistic effect between Na+ and Cl-. This is attributed to the formation of (Na4Cl)3+ clusters that stabilize the sodalite cages. This new finding may be used to increase the selectivity of syntheses leading to FAU-zeolites and avoid the formation of undesirable by-products, especially if impure natural sources of aluminosilica are used.

Site-directed mutagenesis of conserved cysteine residues in NqrD and NqrE subunits of Na+-translocating NADH:quinone oxidoreductase.

PubMed

Fadeeva, M S; Bertsova, Y V; Verkhovsky, M I; Bogachev, A V

2008-02-01

Each of two hydrophobic subunits of Na+-translocating NADH:quinone oxidoreductase (NQR), NqrD and NqrE, contain a pair of strictly conserved cysteine residues within their transmembrane alpha-helices. Site-directed mutagenesis showed that substitutions of these residues in NQR of Vibrio harveyi blocked the Na+-dependent and 2-n-heptyl-4-hydroxyquinoline N-oxide-sensitive quinone reductase activity of the enzyme. However, these mutations did not affect the interaction of NQR with NADH and menadione. It was demonstrated that these conserved cysteine residues are necessary for the correct folding and/or the stability of the NQR complex. Mass and EPR spectroscopy showed that NQR from V. harveyi bears only a 2Fe-2S cluster as a metal-containing prosthetic group.

Reversible emission evolution from Ag activated zeolite Na-A upon dehydration/hydration

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

Lin, Hui, E-mail: linh8112@163.com, E-mail: fujii@eedept.kobe-u.ac.jp; Imakita, Kenji; Fujii, Minoru, E-mail: linh8112@163.com, E-mail: fujii@eedept.kobe-u.ac.jp

2014-11-24

Reversible emission evolution of thermally treated Ag activated zeolite Na-A upon dehydration/hydration in vacuum/water vapor was observed. The phenomenon was observed even for the sample with low Ag{sup +}-Na{sup +} exchanging (8.3%), indicating that the emission from Ag activated zeolites may not come from Ag clusters while from the surrounding coordinated Ag{sup +} ions or Ag{sup 0} atoms. It was disclosed that the characteristic yellow-green emission at ∼560 ± 15 nm is strongly associated with the coordinating water molecules to the Ag{sup +} ions or Ag{sup 0} atoms, which is clear evidence for that the efficient emission from Ag activated zeolites may notmore » originate from the quantum confinement effect.« less

High performance electrolytes for MCFC

DOEpatents

Kaun, T.D.; Roche, M.F.

1999-08-24

A carbonate electrolyte of the Li/Na or CaBaLiNa system is described. The Li/Na carbonate has a composition displaced from the eutectic composition to diminish segregation effects in a molten carbonate fuel cell. The CaBaLiNa system includes relatively small amounts of Ca{sub 2}CO{sub 3} and BaCO{sub 3}, and preferably of equimolar amounts. The presence of both Ca and BaCO{sub 3} enables lower temperature fuel cell operation. 15 figs.

Quantum chemical study of small AlnBm clusters: Structure and physical properties

NASA Astrophysics Data System (ADS)

Loukhovitski, Boris I.; Sharipov, Alexander S.; Starik, Alexander M.

2017-08-01

The structure and physical properties, including rotational constants, characteristic vibrational temperatures, collision diameter, dipole moment, static polarizability, the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), and formation enthalpy of the different isomeric forms of AlnBm clusters with n + m ⩽ 7 are studied using density functional theory. The search of the structure of isomers has been carried employing multistep hierarchical algorithm. Temperature dependencies of thermodynamic functions, such as enthalpy, entropy, and specific heat capacity, have been determined both for the individual isomers and for the ensembles with equilibrium and frozen compositions for the each class of clusters taking into account the anharmonicity of cluster vibrations and the contribution of their excited electronic states. The prospects of the application of small AlnBm clusters as the components of energetic materials are also considered.

Near-Infrared Spectroscopy of Small Protonated Water Clusters

NASA Astrophysics Data System (ADS)

Wagner, J. Philipp; McDonald, David C., II; McCoy, Anne B.; Duncan, Michael A.

2017-06-01

Small protonated water clusters and their argon tagged analogues of the general formula H^{+}(H_{2}O)_{n}Ar_{m} have been generated in a pulsed electric discharge source. Clusters containing n=1-8 water molecules were mass-selected and their absorptions in the near-infrared were probed with a tunable Nd/colonYAG pumped OPA/OPA laser system in the region from 4850-7350 cm^{-1}. A doublet corresponding to overtones of the free O-H stretches of the external waters was observed around 7200 cm^{-1} that was continuously decreasing in intensity with increasing cluster size. Broad, mostly featureless absorptions were found around 5300 cm^{-1} associated with stretch/bend combinations and with the hydrogen bonded waters in the core of the clusters. Vibrational assignments were substantiated by comparison to anharmonic frequency computations via second-order vibrational perturbation theory (VPT2) at the MP2/aug-cc-pVTZ level of theory.

Sodium sulfate-induced corrosion of pure nickel and superalloy Udimet 700 in a high velocity burner rig at 900 C

NASA Technical Reports Server (NTRS)

Misra, A. K.

1987-01-01

Sodium sulfate-induced corrosion of pure nickel and a commercial nickel-base superalloy, Udimet 700 (U-700), were studied at 900 C in a Mach 0.3 burner rig with different Na levels in the combustor. The corrosion rate of Ni was independent of the Na level in the combustor and considerably lower than that measured in laboratory salt spray tests. The lower rates are associated with the deposition of only a small amount of Na2SO4 on the surface of the NiO scale. Corrosion of U-700 was observed to occur in two stages. During the first stage, the corrosion proceeds by reaction of Cr2O3 scale with the Na2SO4 and evaporation of the Na2CrO4 reaction product from the surface of the corroding sample. Cr depletion in the alloy occurs and small sulfide particles are formed in the Cr depletion zone. Extensive sulfidation occurs during the second state of corrosion, and a thick scale forms. The relationship between the corrosion rate of U-700 and the Na level in the combustor gives a good correlation in the range of 0.3 to 1.5 ppm by weight Na. Very low levels of Na in the combustor cause accelerated oxidation of U-700 without producing the typical hot corrosion morphology.

Peripheral CD4+ naïve/memory ratio is an independent predictor of survival in non-small cell lung cancer

PubMed Central

Yang, Peng; Ma, Junhong; Yang, Xin; Li, Wei

2017-01-01

Background To investigate the clinical significance of naïve T cells, memory T cells, CD45RA+CD45RO+ T cells, and naïve/memory ratio in non-small cell lung cancer (NSCLC) patients. Methods Pretreatment peripheral blood samples from 76 NSCLC patients and 28 age- and sex-matched healthy volunteers were collected and tested for immune cells by flow cytometry. We compared the expression of these immune cells between patients and healthy controls and evaluated their predictive roles for survival in NSCLC by cox proportional hazards model. Results Decreased naïve CD4+ T cells, naïve CD8+ T cells, CD4+ naïve/memory ratios and CD4+CD45RA+CD45RO+ T cells, and increased memory CD4+ T cells, were observed in 76 NSCLC patients compared to healthy volunteers. Univariate analysis revealed that elevated CD4+ naïve/memory ratio correlated with prolonged progression-free survival (P=0.013). Multivariate analysis confirmed its predictive role with a hazard ratio of 0.35 (95% confidence interval, 0.19-0.75, P=0.012). Conclusions Peripheral CD4+ naïve/memory ratio can be used as a predictive biomarker in NSCLC patients and used to optimize personalized treatment strategies. PMID:29137371

Characterization and Genome Analysis of a Nicotine and Nicotinic Acid-Degrading Strain Pseudomonas putida JQ581 Isolated from Marine.

PubMed

Li, Aiwen; Qiu, Jiguo; Chen, Dongzhi; Ye, Jiexu; Wang, Yuhong; Tong, Lu; Jiang, Jiandong; Chen, Jianmeng

2017-05-31

The presence of nicotine and nicotinic acid (NA) in the marine environment has caused great harm to human health and the natural environment. Therefore, there is an urgent need to use efficient and economical methods to remove such pollutants from the environment. In this study, a nicotine and NA-degrading bacterium-strain JQ581-was isolated from sediment from the East China Sea and identified as a member of Pseudomonas putida based on morphology, physio-biochemical characteristics, and 16S rDNA gene analysis. The relationship between growth and nicotine/NA degradation suggested that strain JQ581 was a good candidate for applications in the bioaugmentation treatment of nicotine/NA contamination. The degradation intermediates of nicotine are pseudooxynicotine (PN) and 3-succinoyl-pyridine (SP) based on UV, high performance liquid chromatography, and liquid chromatography-mass spectrometry analyses. However, 6-hydroxy-3-succinoyl-pyridine (HSP) was not detected. NA degradation intermediates were identified as 6-hydroxynicotinic acid (6HNA). The whole genome of strain JQ581 was sequenced and analyzed. Genome sequence analysis revealed that strain JQ581 contained the gene clusters for nicotine and NA degradation. This is the first report where a marine-derived Pseudomonas strain had the ability to degrade nicotine and NA simultaneously.

Elucidation of Proton-Assisted Fluxionality in Transition-Metal Oxide Clusters

NASA Astrophysics Data System (ADS)

Ramabhadran, Raghunath O.; Mayhall, Nicholas J.; Becher, Edwin L. Becher, Iii; Chowdhury, Arefin; Raghavachari, Krishnan

2012-06-01

The phenomenon of fluxionality in the reactions of transition-metal oxide clusters provides many opportunities in various industrial and catalytic processes. We present an electronic structure investigation of the fluxionality pathways when anionic W3O6- and Mo3O6- clusters react with three small molecules - water, ammonia and hydrogen sulfide. The presentation features a detailed understanding of (a) how the fluxionality pathway occurs and (b) the various factors that affect the fluxionality pathway - such as the metal, different spin-states and the nature of the non-metal in the reacting small molecule.

Facile Syntheses of Monodisperse Ultra-Small Au Clusters

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

Bertino, Massimo F.; Sun, Zhong-Ming; Zhang, Rui

2006-11-02

During our effort to synthesize the tetrahedral Au20 cluster, we found a facile synthetic route to prepare monodisperse suspensions of ultra-small Au clusters AuN (N<12) using diphosphine ligands. In our monophasic and single-pot synthesis, a Au precursor ClAu(I)PPh3 and a bidentate phosphine ligand P(Ph)2(CH2)MP(Ph)2 (Ph = phenyl) are dissolved in an organic solvent. Au(I) is reduced slowly by a borane-tert-butylamine complex to form Au clusters coordinated by the diphosphine ligand. The Au clusters are characterized by both high resolution mass spectrometry and UV-Vis absorption spectroscopy. We found that the mean cluster size obtained depends on the chain length M ofmore » the ligand. In particular, a single monodispersed Au11 cluster is obtained with the P(Ph)2(CH2)3P(Ph)2 ligand, whereas P(Ph)2(CH2)MP(Ph)2 ligands with M = 5 and 6 yield Au10 and Au8 clusters. The simplicity of our synthetic method makes it suitable for large-scale production of nearly monodisperse ultrasmall Au clusters. It is suggested that diphosphines provide a set of flexible ligands to allow size-controlled synthesis of Au nanoparticles.« less

Self-Printing on Graphitic Nanosheets with Metal Borohydride Nanodots for Hydrogen Storage

NASA Astrophysics Data System (ADS)

Li, Yongtao; Ding, Xiaoli; Zhang, Qingan

2016-08-01

Although the synthesis of borohydride nanostructures is sufficiently established for advancement of hydrogen storage, obtaining ultrasmall (sub-10 nm) metal borohydride nanocrystals with excellent dispersibility is extremely challenging because of their high surface energy, exceedingly strong reducibility/hydrophilicity and complicated composition. Here, we demonstrate a mechanical-force-driven self-printing process that enables monodispersed (~6 nm) NaBH4 nanodots to uniformly anchor onto freshly-exfoliated graphitic nanosheets (GNs). Both mechanical-forces and borohydride interaction with GNs stimulate NaBH4 clusters intercalation/absorption into the graphite interlayers acting as a ‘pen’ for writing, which is accomplished by exfoliating GNs with the ‘printed’ borohydrides. These nano-NaBH4@GNs exhibit favorable thermodynamics (decrease in ΔH of ~45%), rapid kinetics (a greater than six-fold increase) and stable de-/re-hydrogenation that retains a high capacity (up to ~5 wt% for NaBH4) compared with those of micro-NaBH4. Our results are helpful in the scalable fabrication of zero-dimensional complex hydrides on two-dimensional supports with enhanced hydrogen storage for potential applications.

Self-Printing on Graphitic Nanosheets with Metal Borohydride Nanodots for Hydrogen Storage

PubMed Central

Li, Yongtao; Ding, Xiaoli; Zhang, Qingan

2016-01-01

Although the synthesis of borohydride nanostructures is sufficiently established for advancement of hydrogen storage, obtaining ultrasmall (sub-10 nm) metal borohydride nanocrystals with excellent dispersibility is extremely challenging because of their high surface energy, exceedingly strong reducibility/hydrophilicity and complicated composition. Here, we demonstrate a mechanical-force-driven self-printing process that enables monodispersed (~6 nm) NaBH4 nanodots to uniformly anchor onto freshly-exfoliated graphitic nanosheets (GNs). Both mechanical-forces and borohydride interaction with GNs stimulate NaBH4 clusters intercalation/absorption into the graphite interlayers acting as a ‘pen’ for writing, which is accomplished by exfoliating GNs with the ‘printed’ borohydrides. These nano-NaBH4@GNs exhibit favorable thermodynamics (decrease in ∆H of ~45%), rapid kinetics (a greater than six-fold increase) and stable de-/re-hydrogenation that retains a high capacity (up to ~5 wt% for NaBH4) compared with those of micro-NaBH4. Our results are helpful in the scalable fabrication of zero-dimensional complex hydrides on two-dimensional supports with enhanced hydrogen storage for potential applications. PMID:27484735

Nurse Aide. Occupational Competency Analysis Profile.

ERIC Educational Resources Information Center

Ohio State Univ., Columbus. Vocational Instructional Materials Lab.

This Occupational Competency Analysis Profile (OCAP) for nurse aide (NA) is a competency list verified by expert workers that evolved from a job analysis. It identifies occupational, academic, and employability competencies needed to enter the occupation; lists and clusters them into broader units; and details the competency builders needed to…

FAST TRACK COMMUNICATION Accurate estimate of α variation and isotope shift parameters in Na and Mg+

NASA Astrophysics Data System (ADS)

Sahoo, B. K.

2010-12-01

We present accurate calculations of fine-structure constant variation coefficients and isotope shifts in Na and Mg+ using the relativistic coupled-cluster method. In our approach, we are able to discover the roles of various correlation effects explicitly to all orders in these calculations. Most of the results, especially for the excited states, are reported for the first time. It is possible to ascertain suitable anchor and probe lines for the studies of possible variation in the fine-structure constant by using the above results in the considered systems.

Development of a high-sensitivity BGO well counter for small animal PET studies.

PubMed

Yamamoto, Seiichi; Watabe, Hiroshi; Kanai, Yasukazu; Watabe, Tadashi; Imaizumi, Masao; Shimosegawa, Eku; Hatazawa, Jun

2012-01-01

In quantitative measurements of small animal PET studies, blood sampling is limited due to the small amounts of blood such animals can provide. In addition, injection doses are quite limited. In this situation, a high-sensitivity well counter would be useful for reducing the amount of the blood sample needed from small animals. Bismuth germinate (BGO) has a high stopping power for high-energy gamma rays compared to NaI(Tl), which is commonly used for conventional well counters. We have developed a BGO well counter and have tested it for blood-sampling measurements in small animals. The BGO well counter uses a square BGO block (59 × 59 × 50 mm) with a square open space (27 × 27 × 34 mm) in the center of the block. The BGO block was optically coupled to a 59-mm square-shaped photomultiplier tube (PMT). Signals from the PMT were digitally processed for the integration and energy window setting. The results showed that the energy spectrum of the BGO well counter measured with a Na-22 point source provided counts that were about 6 times higher for a 1022-keV (511 keV × 2) gamma peak than the spectrum of a 2-in. NaI(Tl) well counter. The relative sensitivity of the developed BGO well counter was 3.4 times higher than that of a NaI(Tl) well counter. The time activity curve of arterial blood was obtained successfully with the BGO well counter for a F-18-FDG study on rat. The BGO well counter will contribute to reducing the amount of sampled blood and to improving the throughput of quantitative measurements in small animal PET studies.

The absorption and first-pass metabolism of [14C]-1,3-dinitrobenzene in the isolated vascularly perfused rat small intestine.

PubMed

Adams, P C; Rickert, D E

1996-11-01

We tested the hypothesis that the small intestine is capable of the first-pass, reductive metabolism of xenobiotics. A simplified version of the isolated vascularly perfused rat small intestine was developed to test this hypothesis with 1,3-dinitrobenzene (1,3-DNB) as a model xenobiotic. Both 3-nitroaniline (3-NA) and 3-nitroacetanilide (3-NAA) were formed and absorbed following intralumenal doses of 1,3-DNB (1.8 or 4.2 mumol) to isolated vascularly perfused rat small intestine. Dose, fasting, or antibiotic pretreatment had no effect on the absorption and metabolism of 1,3-DNB in this model system. The failure of antibiotic pretreatment to alter the metabolism of 1,3-DNA indicated that 1,3-DNB metabolism was mammalian rather than microfloral in origin. All data from experiments initiated with lumenal 1,3-DNB were fit to a pharmacokinetic model (model A). ANOVA analysis revealed that dose, fasting, or antibiotic pretreatment had no statistically significant effect on the model-dependent parameters. 3-NA (1.5 mumol) was administered to the lumen of isolated vascularly perfused rat small intestine to evaluate model A predictions for the absorption and metabolism of this metabolite. All data from experiments initiated with 3-NA were fit to a pharmacokinetic model (model B). Comparison of corresponding model-dependent pharmacokinetic parameters (i.e. those parameters which describe the same processes in models A and B) revealed quantitative differences. Evidence for significant quantitative differences in the pharmacokinetics or metabolism of formed versus preformed 3-NA in rat small intestine may require better definition of the rate constants used to describe tissue and lumenal processes or identification and incorporation of the remaining unidentified metabolites into the models.

Binomial outcomes in dataset with some clusters of size two: can the dependence of twins be accounted for? A simulation study comparing the reliability of statistical methods based on a dataset of preterm infants.

PubMed

Sauzet, Odile; Peacock, Janet L

2017-07-20

The analysis of perinatal outcomes often involves datasets with some multiple births. These are datasets mostly formed of independent observations and a limited number of clusters of size two (twins) and maybe of size three or more. This non-independence needs to be accounted for in the statistical analysis. Using simulated data based on a dataset of preterm infants we have previously investigated the performance of several approaches to the analysis of continuous outcomes in the presence of some clusters of size two. Mixed models have been developed for binomial outcomes but very little is known about their reliability when only a limited number of small clusters are present. Using simulated data based on a dataset of preterm infants we investigated the performance of several approaches to the analysis of binomial outcomes in the presence of some clusters of size two. Logistic models, several methods of estimation for the logistic random intercept models and generalised estimating equations were compared. The presence of even a small percentage of twins means that a logistic regression model will underestimate all parameters but a logistic random intercept model fails to estimate the correlation between siblings if the percentage of twins is too small and will provide similar estimates to logistic regression. The method which seems to provide the best balance between estimation of the standard error and the parameter for any percentage of twins is the generalised estimating equations. This study has shown that the number of covariates or the level two variance do not necessarily affect the performance of the various methods used to analyse datasets containing twins but when the percentage of small clusters is too small, mixed models cannot capture the dependence between siblings.

Effect of silver ions and clusters on the luminescence properties of Eu-doped borate glasses

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

Jiao, Qing, E-mail: jiaoqing@nbu.edu.cn; Wang, Xi; Qiu, Jianbei

2015-12-15

Highlights: • Ag{sup +} and Ag clusters are investigated in the borate glasses via ion exchange method. • The aggregation of silver ions to the clusters was controlled by the ion exchange concentration. • Eu{sup 3+}/Eu{sup 2+} ions emission was enhanced with the sensitization of the silver species. • Energy transfer process from Ag ions and Ag clusters to Eu ions is identified by the lifetime measurements. - Abstract: Silver ions and clusters were applied to Eu{sup 3+}-doped borate glasses via the Ag{sup +}–Na{sup +} ion exchange method. Eu{sup 3+}/Eu{sup 2+} ion luminescence enhancement was achieved after silver ion exchange.more » Absorption spectra showed no band at 420 nm, which indicates that silver nanoparticles can be excluded as a silver state in the glass. Silver ion aggregation into clusters during the ion exchange process may be inferred. The effect of silver ions and clusters on rare earth emissions was investigated using spectral information and lifetime measurements. Significant luminescence enhancements were observed from the energy transfer of Ag{sup +} ions and clusters to Eu{sup 3+}/Eu{sup 2+} ions, companied with the silver ions aggregated into the clusters state. The results of this research may extend the current understanding of interactions between rare-earth ions and Ag species.« less

Sensitivity of Rabbit Ventricular Action Potential and Ca2+ Dynamics to Small Variations in Membrane Currents and Ion Diffusion Coefficients

PubMed Central

Lo, Yuan Hung; Peachey, Tom; Abramson, David; McCulloch, Andrew

2013-01-01

Little is known about how small variations in ionic currents and Ca2+ and Na+ diffusion coefficients impact action potential and Ca2+ dynamics in rabbit ventricular myocytes. We applied sensitivity analysis to quantify the sensitivity of Shannon et al. model (Biophys. J., 2004) to 5%–10% changes in currents conductance, channels distribution, and ion diffusion in rabbit ventricular cells. We found that action potential duration and Ca2+ peaks are highly sensitive to 10% increase in L-type Ca2+ current; moderately influenced by 10% increase in Na+-Ca2+ exchanger, Na+-K+ pump, rapid delayed and slow transient outward K+ currents, and Cl− background current; insensitive to 10% increases in all other ionic currents and sarcoplasmic reticulum Ca2+ fluxes. Cell electrical activity is strongly affected by 5% shift of L-type Ca2+ channels and Na+-Ca2+ exchanger in between junctional and submembrane spaces while Ca2+-activated Cl−-channel redistribution has the modest effect. Small changes in submembrane and cytosolic diffusion coefficients for Ca2+, but not in Na+ transfer, may alter notably myocyte contraction. Our studies highlight the need for more precise measurements and further extending and testing of the Shannon et al. model. Our results demonstrate usefulness of sensitivity analysis to identify specific knowledge gaps and controversies related to ventricular cell electrophysiology and Ca2+ signaling. PMID:24222910

Effect of small versus large clusters of fish school on the yield of a purse-seine small pelagic fishery including a marine protected area.

PubMed

Hieu, Nguyen Trong; Brochier, Timothée; Tri, Nguyen-Huu; Auger, Pierre; Brehmer, Patrice

2014-09-01

We consider a fishery model with two sites: (1) a marine protected area (MPA) where fishing is prohibited and (2) an area where the fish population is harvested. We assume that fish can migrate from MPA to fishing area at a very fast time scale and fish spatial organisation can change from small to large clusters of school at a fast time scale. The growth of the fish population and the catch are assumed to occur at a slow time scale. The complete model is a system of five ordinary differential equations with three time scales. We take advantage of the time scales using aggregation of variables methods to derive a reduced model governing the total fish density and fishing effort at the slow time scale. We analyze this aggregated model and show that under some conditions, there exists an equilibrium corresponding to a sustainable fishery. Our results suggest that in small pelagic fisheries the yield is maximum for a fish population distributed among both small and large clusters of school.

Measurement of the spectral signature of small carbon clusters at near and far infrared wavelengths

NASA Technical Reports Server (NTRS)

Tarter, J.; Saykally, R.

1991-01-01

A significant percentage of the carbon inventory of the circumstellar and interstellar media may be in the form of large refractory molecules (or small grains) referred to as carbon clusters. At the small end, uneven numbers of carbon atoms seem to be preferred, whereas above 12 atoms, clusters containing an even number of carbon atoms appear to be preferred in laboratory chemistry. In the lab, the cluster C-60 appears to be a particularly stable form and has been nicknamed Bucky Balls because of its resemblance to a soccer ball and to geodesic domes designed by Buckminster Fuller. In order to investigate the prevalence of these clusters, and their relationship to the polycyclic aromatic hydrocarbons (PAHs) that have become the newest focus of IR astronomy, it is necessary to determine the spectroscopic characteristics of these clusters at near and far infrared wavelengths. Described here is the construction of a near to far IR laser magnetic resonance spectrometer that has been built at the University of California Berkeley in order to detect and characterize these spectra. The equipment produces carbon clusters by laser evaporation of a graphitic target. The clusters are then cooled in a supersonic expansion beam in order to simulate conditions in the interstellar medium (ISM). The expansion beam feeds into the spectrometer chamber and permits concentrations of clusters sufficiently high as to permit ultra-high resolution spectroscopy at near and far IR wavelengths. The first successful demonstration of this apparatus occurred last year when the laboratory studies permitted the observational detection of C-5 in the stellar outflow surrounding IRC+10216 in the near-IR. Current efforts focus on reducing the temperature of the supersonic expansion beam that transport the C clusters evaporated from a graphite target into the spectrometer down to temperatures as low as 1 K.

Comparison of the effects of intravenous administration of isotonic and hypertonic sodium bicarbonate solutions on venous acid-base status in dehydrated calves with strong ion acidosis.

PubMed

Coskun, Alparslan; Sen, Ismail; Guzelbektes, Hasan; Ok, Mahmut; Turgut, Kursat; Canikli, Sebnem

2010-05-15

OBJECTIVE-To compare the effects of IV administration of isotonic (1.3%) and hypertonic (8.4%) sodium bicarbonate (NaHCO(3)) solutions on acid-base status in dehydrated calves with strong ion (metabolic) acidosis. DESIGN-Randomized controlled clinical trial. ANIMALS-50 calves with diarrhea and severe dehydration. PROCEDURES-Calves were randomly assigned to receive isotonic NaHCO(3) solution (65 mL/kg [29.5 mL/lb], IV) over 3 hours (n = 30) or hypertonic NaHCO(3) solution (10 mL/kg [4.5 mL/lb], IV) over 20 minutes (20). Blood samples were collected at 0 hours (immediately prior to solution administration) and at 0.5, 1, 2, and 4 hours after administration began. Samples were submitted for blood gas analysis, serum biochemical analysis, and determination of blood Na(+), K(+), and Cl(-) concentrations and percentage change in plasma volume. RESULTS-Calves that received isotonic NaHCO(3) solution had an increase in venous blood pH, HCO(3) concentration, and base excess; a small, transient increase in Po(2); and no change in Pco(2) within 4 hours after administration began. Calves that received hypertonic NaHCO(3) solution had an immediate increase in venous blood pH, HCO(3) concentration, and base excess; a small, transient increase Pco(2); and no change in Po(2) within 0.5 hours after treatment began. Plasma volume increased to a greater extent following administration of isotonic solution than after administration of hypertonic solution. CONCLUSIONS AND CLINICAL RELEVANCE-IV administration of 8.4% NaHCO(3) solution in small volumes provided fast and effective improvement of severe acid-base abnormalities in calves with severe strong ion acidosis but did not improve hydration status as well as administration of a larger volume of isotonic NaHCO(3) solution.

Antecedent hydrogen sulfide elicits an anti-inflammatory phenotype in postischemic murine small intestine: role of BK channels

PubMed Central

Zuidema, Mozow Y.; Yang, Yan; Wang, Meifang; Kalogeris, Theodore; Liu, Yajun; Meininger, Cynthia J.; Hill, Michael A.; Davis, Michael J.

2010-01-01

The objectives of this study were to determine the role of calcium-activated, small (SK), intermediate (IK), and large (BK) conductance potassium channels in initiating the development of an anti-inflammatory phenotype elicited by preconditioning with an exogenous hydrogen sulfide (H2S) donor, sodium hydrosulfide (NaHS). Intravital microscopy was used to visualize rolling and firmly adherent leukocytes in vessels of the small intestine of mice preconditioned with NaHS (in the absence and presence of SK, IK, and BK channel inhibitors, apamin, TRAM-34, and paxilline, respectively) or SK/IK (NS-309) or BK channel activators (NS-1619) 24 h before ischemia-reperfusion (I/R). I/R induced marked increases in leukocyte rolling and adhesion, effects that were largely abolished by preconditioning with NaHS, NS-309, or NS-1619. The postischemic anti-inflammatory effects of NaHS-induced preconditioning were mitigated by BKB channel inhibitor treatment coincident with NaHS, but not by apamin or TRAM-34, 24 h before I/R. Confocal imaging and immunohistochemistry were used to demonstrate the presence of BKα subunit staining in both endothelial and vascular smooth muscle cells of isolated, pressurized mesenteric venules. Using patch-clamp techniques, we found that BK channels in cultured endothelial cells were activated after exposure to NaHS. Bath application of the same concentration of NaHS used in preconditioning protocols led to a rapid increase in a whole cell K+ current; specifically, the component of K+ current blocked by the selective BK channel antagonist iberiotoxin. The activation of BK current by NaHS could also be demonstrated in single channel recording mode where it was independent of a change in intracellular Ca+ concentration. Our data are consistent with the concept that H2S induces the development of an anti-adhesive state in I/R in part mediated by a BK channel-dependent mechanism. PMID:20833953

A hierarchical cluster analysis of normal-tension glaucoma using spectral-domain optical coherence tomography parameters.

PubMed

Bae, Hyoung Won; Ji, Yongwoo; Lee, Hye Sun; Lee, Naeun; Hong, Samin; Seong, Gong Je; Sung, Kyung Rim; Kim, Chan Yun

2015-01-01

Normal-tension glaucoma (NTG) is a heterogenous disease, and there is still controversy about subclassifications of this disorder. On the basis of spectral-domain optical coherence tomography (SD-OCT), we subdivided NTG with hierarchical cluster analysis using optic nerve head (ONH) parameters and retinal nerve fiber layer (RNFL) thicknesses. A total of 200 eyes of 200 NTG patients between March 2011 and June 2012 underwent SD-OCT scans to measure ONH parameters and RNFL thicknesses. We classified NTG into homogenous subgroups based on these variables using a hierarchical cluster analysis, and compared clusters to evaluate diverse NTG characteristics. Three clusters were found after hierarchical cluster analysis. Cluster 1 (62 eyes) had the thickest RNFL and widest rim area, and showed early glaucoma features. Cluster 2 (60 eyes) was characterized by the largest cup/disc ratio and cup volume, and showed advanced glaucomatous damage. Cluster 3 (78 eyes) had small disc areas in SD-OCT and were comprised of patients with significantly younger age, longer axial length, and greater myopia than the other 2 groups. A hierarchical cluster analysis of SD-OCT scans divided NTG patients into 3 groups based upon ONH parameters and RNFL thicknesses. It is anticipated that the small disc area group comprised of younger and more myopic patients may show unique features unlike the other 2 groups.

Low-temperature cluster catalysis.

PubMed

Judai, Ken; Abbet, Stéphane; Wörz, Anke S; Heiz, Ulrich; Henry, Claude R

2004-03-10

Free and supported metal clusters reveal unique chemical and physical properties, which vary as a function of size as each cluster possesses a characteristic electron confinement. Several previous experimental results showed that the outcome of a given chemical reaction can be controlled by tuning the cluster size. However, none of the examples indicate that clusters prepared in the gas phase and then deposited on a support material are indeed catalytically active over several reaction cycles nor that their catalytic properties remain constant during such a catalytic process. In this work we report turn-over frequencies (TOF) for Pd(n) (n = 4, 8, 30) clusters using pulsed molecular beam experiments. The obtained results illustrate that the catalytic reactivity for the NO reduction by CO (CO + NO --> 1/2N(2) + CO(2)) is indeed a function of cluster size and that the measured TOF remain constant at a given temperature. More interestingly, the temperature of maximal reactivity is at least 100 K lower than observed for palladium nanoparticles or single crystals. One reason for this surprising observation is the character of the binding sites of these small clusters: N(2) forms already at relatively low temperatures (400 and 450 K) and therefore poisoning by adsorbed nitrogen adatoms is prevented. Thus, small clusters not only open the possibility of tuning a catalytic process by changing cluster size, but also of catalyzing chemical reactions at low temperatures.

Effects of catalase on chloroplast arrangement in Opuntia streptacantha chlorenchyma cells under salt stress.

PubMed

Arias-Moreno, Diana Marcela; Jiménez-Bremont, Juan Francisco; Maruri-López, Israel; Delgado-Sánchez, Pablo

2017-08-17

In arid and semiarid regions, low precipitation rates lead to soil salinity problems, which may limit plant establishment, growth, and survival. Herein, we investigated the NaCl stress effect on chlorophyll fluorescence, photosynthetic-pigments, movement and chloroplasts ultrastructure in chlorenchyma cells of Opuntia streptacantha cladodes. Cladodes segments were exposed to salt stress at 0, 100, 200, and 300 mM NaCl for 8, 16, and 24 h. The results showed that salt stress reduced chlorophyll content, F v /F m , ΦPSII, and qP values. Under the highest salt stress treatments, the chloroplasts were densely clumped toward the cell center and thylakoid membranes were notably affected. We analyzed the effect of exogenous catalase in salt-stressed cladode segments during 8, 16, and 24 h. The catalase application to salt-stressed cladodes counteracted the NaCl adverse effects, increasing the chlorophyll fluorescence parameters, photosynthetic-pigments, and avoided chloroplast clustering. Our results indicate that salt stress triggered the chloroplast clumping and affected the photosynthesis in O. streptacantha chlorenchyma cells. The exogenous catalase reverted the H 2 O 2 accumulation and clustering of chloroplast, which led to an improvement of the photosynthetic efficiency. These data suggest that H 2 O 2 detoxification by catalase is important to protect the chloroplast, thus conserving the photosynthetic activity in O. streptacantha under stress.

The Aftermath of a Suicide Cluster in the Age of Online Social Networking: A Qualitative Analysis of Adolescent Grief Reactions

ERIC Educational Resources Information Center

Heffel, Carly J.; Riggs, Shelley A.; Ruiz, John M.; Ruggles, Mark

2015-01-01

Although suicide clusters have been identified in many populations, research exploring the role of online communication in the aftermath of a suicide cluster is extremely limited. This study used the Consensual Qualitative Research method to analyze interviews with ten high school students 1 year after a suicide cluster in a small suburban school…

Properties of Diamond and Diamond-Like Clusters in Nanometric Dimensions

NASA Technical Reports Server (NTRS)

Halicioglu, Timur; Langhoff, Stephen R. (Technical Monitor)

1996-01-01

Variations in materials properties of small clusters of nanometric dimensions were investigated. Investigations were carried out for diamond and diamond-like particles in spherical shapes. Calculations were performed for clusters containing over 1000 carbon atoms. Results indicate that as the cluster size diminishes, (i) the average cohesive energy becomes weaker, (ii) the excess surface energy increases, and (iii) the value for stiffness decreases.

Derivatized gold clusters and antibody-gold cluster conjugates

DOEpatents

Hainfeld, J.F.; Furuya, F.R.

1994-11-01

Antibody- or antibody fragment-gold cluster conjugates are shown wherein the conjugate size can be as small as 5.0 nm. Methods and reagents are disclosed in which antibodies, Fab' or F(ab')[sub 2] fragments are covalently bound to a stable cluster of gold atoms. The gold clusters may contain 6, 8, 9, 11, 13, 55 or 67 gold atoms in their inner core. The clusters may also contain radioactive gold. The antibody-cluster conjugates are useful in electron microscopy applications as well as in clinical applications that include imaging, diagnosis and therapy. 7 figs.

The Distribution and Ages of Star Clusters in the Small Magellanic Cloud: Constraints on the Interaction History of the Magellanic Clouds

NASA Astrophysics Data System (ADS)

Bitsakis, Theodoros; González-Lópezlira, R. A.; Bonfini, P.; Bruzual, G.; Maravelias, G.; Zaritsky, D.; Charlot, S.; Ramírez-Siordia, V. H.

2018-02-01

We present a new study of the spatial distribution and ages of the star clusters in the Small Magellanic Cloud (SMC). To detect and estimate the ages of the star clusters we rely on the new fully automated method developed by Bitsakis et al. Our code detects 1319 star clusters in the central 18 deg2 of the SMC we surveyed (1108 of which have never been reported before). The age distribution of those clusters suggests enhanced cluster formation around 240 Myr ago. It also implies significant differences in the cluster distribution of the bar with respect to the rest of the galaxy, with the younger clusters being predominantly located in the bar. Having used the same setup, and data from the same surveys as for our previous study of the LMC, we are able to robustly compare the cluster properties between the two galaxies. Our results suggest that the bulk of the clusters in both galaxies were formed approximately 300 Myr ago, probably during a direct collision between the two galaxies. On the other hand, the locations of the young (≤50 Myr) clusters in both Magellanic Clouds, found where their bars join the H I arms, suggest that cluster formation in those regions is a result of internal dynamical processes. Finally, we discuss the potential causes of the apparent outside-in quenching of cluster formation that we observe in the SMC. Our findings are consistent with an evolutionary scheme where the interactions between the Magellanic Clouds constitute the major mechanism driving their overall evolution.

Analysis of Nanoprecipitates in a Na-Doped PbTe-SrTe Thermoelectric Material with a High Figure of Merit.

PubMed

Kim, Yoon-Jun; Zhao, Li-Dong; Kanatzidis, Mercouri G; Seidman, David N

2017-07-05

The dimensionless figure of merit, ZT, of bulk thermoelectric materials depends mainly on the transport properties of charge carriers and heat-carrying phonons. PbTe-4 mol % SrTe doped with 2 mol % Na (Pb 0.94 Na 0.02 Sr 0.04 Te) is a nanostructured material system that exhibits a ZT higher than 2. The precipitate size distribution of SrTe precipitates is believed to play a key role. This raises the question of whether its performance is limited by precipitate coarsening (Ostwald ripening) at elevated temperatures. Herein, we utilize an atom-probe tomography (APT) to study the number density and mean radii of precipitates in concert with partial radial distribution functions (RDFs) of individual atoms. We find that the SrTe precipitates actually contain oxygen: SrTe 1-x O x . We correlate this information with the overall ZT performance, specifically focusing on the electrical and lattice thermal conductivities after isothermal heat treatments at 300 and 400 °C for 7 days, followed by furnace cooling. Comparison of the samples annealed at 400 and 300 °C demonstrates significant coarsening of SrTe 1-x O x precipitates as well as strong segregation of oxygen impurities in the SrTe 1-x O x precipitates. Additionally, on the basis of the partial RDFs, the Na dopant atoms cluster with other Na atoms as well as with Pb, Te, and Sr atoms; clustering depends strongly on the annealing temperature and concomitantly affects the overall ZT values. We found that the coarsening slightly increases the lattice thermal conductivity and also increases the electrical conductivity, thereby having little or even a beneficial effect on the ZT values. Importantly, these findings demonstrate that APT enables quantitative analyses in three dimensions of the PbTe-4 mol % SrTe samples in addition to correlation of their properties with the thermoelectric performance.

A new (4, 6)-connected Cu(I) coordination polymer based on rare tetranuclear [Cu4I2] clusters: Synthesis, crystal structure, luminescent and photocatalytic properties

NASA Astrophysics Data System (ADS)

Cui, Li-Jing; Liu, Chun-Yan; Bian, Ming; Yu, Li-Jun

2018-03-01

A new Cu(I) coordination polymer, namely [Cu5I3(L)2]n (1 HL = 3-(4-pyridyl)-5-(3-pyridyl)-1,2,4-triazolyl), was solvothermally synthesized using CuI, HL and NaI as the starting materials. Single crystal X-ray structural analysis shows that compound 1 features a (4, 6)-connected 3D framework employing rare tetranuclear [Cu4I2] clusters as building subunits. It exhibits intense metal-to-ligand luminescence and excellent photocatalytic activity on degradation of methylene blue (MB).

Non-linear valence electron dynamics in metallic clusters

NASA Astrophysics Data System (ADS)

Calvayrac, F.

This work deals with the response of the valence electrons of simple metal clusters to various excitations, in a purely dynamical context. It is related to various recent experiments where the methods based on linear response fail. The electronic motion is solved in direct time, the wavefunctions being discretized on an evenly spaced grid. The theoretical framework is the time dependent density functional theory, restricted to a version local in time and space (LSDA). The other parts of the clusters are either a jellium or an explicit ionic background exerting local or non-local pseudopotentials. The ionic dynamics is discussed, as well as the relevance of various observables. The corresponding numerical techniques are given: either a selfconsistent Crank-Nicholson method is used, approximated by an alternate propagation in every space direction, or a method alternating between direct and Fourier space. The equations suggest a parallel treatment. Several examples of application are given. The case of Na9+ is thoroughly discussed, then the less simple case of Na11+. Spectra obtained for sodium clusters deposited on sodium chlorine surfaces are shown. An example of a simulation with a moving ionic background is handled: the transfer to the ionic degrees of freedom of the energy deposited in a twelve sodium atoms cluster by a femtosecond laser pulse is discussed. The electronic resonance spectrum for a linear carbon cluster C5 is then given. In the conclusion, the work is discussed as well as possible improvements and developments from the theoretical or numerical point of view. Ce travail aborde la réponse des électrons de valence d'agrégats de métaux simples à diverses excitations, dans un contexte purement dynamique, en relation avec diverses expériences récentes que les méthodes fondées sur la réponse linéaire sont incapables d'aborder. Le mouvement de ces électrons est résolu directement en temps, leurs fonctions d'onde étant discrétisées sur une grille régulière en espace. Le cadre théorique repose sur la théorie de la fonctionnelle de la densité dépendant du temps, restreinte à une version locale en temps et en espace (LSDA). Les autres constituants des agrégats sont soit un “jellium”, soit un fond ionique explicite agissant par des pseudopotentiels locaux ou non-locaux. La dynamique de ce fond ionique est discutée, ainsi que la pertinence de différentes observables. Les techniques numériques correspondantes sont présentées. Il s'agit soit d'un traitement Crank-Nicholson autocohérent, approché par une propagation successive dans chacune des directions d'espace, soit d'un traitement alternant entre l'espace direct et celui de Fourier. Les équations utilisées suggèrent un traitement parallèle. Plusieurs exemples d'application sont alors donnés. Nous discutons en détail le cas de Na9^+, puis le cas moins simple de Na{11}^+. Nous donnons des spectres obtenus pour des agrégats de sodium déposés sur une surface de chlorure de sodium. Puis, nous abordons un exemple de simulation avec fond ionique mouvant par dynamique moléculaire. Nous discutons ainsi le transfert aux ions de l'énergie déposée par un laser femtoseconde dans un agrégat Na12. Nous présentons enfin le spectre obtenu pour la résonance électronique dans un agrégat de carbone linéaire C5. Nous concluons alors sur le travail effectué et les développements ou améliorations possibles sur le plan théorique comme numérique.

Investigating the role of small vent volcanism during the development of Tharsis Province, Mars

NASA Astrophysics Data System (ADS)

Richardson, J. A.; Bleacher, J. E.; Connor, C.; Connor, L.; Glaze, L. S.

2014-12-01

Clusters of tens to hundreds of small volcanic vents have recently been recognized as a major component of Tharsis Province volcanism. These volcanic fields are formed from distributed-style, possibly monogenetic, volcanism and are composed of low sloped edifices with diameters of tens of kilometers and heights of tens to hundreds of meters. We report a new catalog of these small volcanic vents, now available through the USGS Astrogeology Science Center. This catalog was created with the use of gridded topographic data from the Mars Orbiter Laser Altimeter (MOLA) and images from the Thermal Emission Imaging System (THEMIS) and the High Resolution Stereo Camera (HRSC). We are now investigating isolated clusters of distributed volcanism in Tharsis with this dataset. We hypothesize that these clusters are formed from significant magmatic events that played a large role in the development of Tharsis. Currently, the catalog contains 1075 unique volcanic vents in the Tharsis Province. With the catalog, potentially isolated volcano clusters are identified with vent density estimation. Vent intensity for clusters is found to be 1 vent per 1000 sq km or less. Crater retention rates for one such cluster, Syria Planum, indicates that these distributed volcanic systems might continue as long as 700 Ma, or that monogenetic volcanic systems overprint older systems. Using a modified basal outlining algorithm with MOLA gridded data, shield volumes are found to be between 1-20 cubic km. Current results show distributed-style volcanism occuring in Tharsis orders of magnitude more dispersed than analogous volcano clusers on Earth, while individual edifices are found to be an order of magnitude larger than volcanoes in Earth clusters. Proof of concept results are reported for three identified clusters: Arsia Mons Caldera, Syria Planum, and Southern Pavonis Mons.

Performance of small cluster surveys and the clustered LQAS design to estimate local-level vaccination coverage in Mali

PubMed Central

2012-01-01

Background Estimation of vaccination coverage at the local level is essential to identify communities that may require additional support. Cluster surveys can be used in resource-poor settings, when population figures are inaccurate. To be feasible, cluster samples need to be small, without losing robustness of results. The clustered LQAS (CLQAS) approach has been proposed as an alternative, as smaller sample sizes are required. Methods We explored (i) the efficiency of cluster surveys of decreasing sample size through bootstrapping analysis and (ii) the performance of CLQAS under three alternative sampling plans to classify local VC, using data from a survey carried out in Mali after mass vaccination against meningococcal meningitis group A. Results VC estimates provided by a 10 × 15 cluster survey design were reasonably robust. We used them to classify health areas in three categories and guide mop-up activities: i) health areas not requiring supplemental activities; ii) health areas requiring additional vaccination; iii) health areas requiring further evaluation. As sample size decreased (from 10 × 15 to 10 × 3), standard error of VC and ICC estimates were increasingly unstable. Results of CLQAS simulations were not accurate for most health areas, with an overall risk of misclassification greater than 0.25 in one health area out of three. It was greater than 0.50 in one health area out of two under two of the three sampling plans. Conclusions Small sample cluster surveys (10 × 15) are acceptably robust for classification of VC at local level. We do not recommend the CLQAS method as currently formulated for evaluating vaccination programmes. PMID:23057445

Polymorphism in magic-sized Au144(SR)60 clusters

DOE PAGES

Jensen, Kirsten M. O.; Juhas, Pavol; Tofanelli, Marcus A.; ...

2016-06-14

Ultra-small, magic-sized metal nanoclusters represent an important new class of materials with properties between molecules and particles. However, their small size challenges the conventional methods for structure characterization. We present the structure of ultra-stable Au144(SR)60 magic-sized nanoclusters obtained from atomic pair distribution function analysis of X-ray powder diffraction data. Our study reveals structural polymorphism in these archetypal nanoclusters. Additionally, in order to confirm the theoretically predicted icosahedral-cored cluster, we also find samples with a truncated decahedral core structure, with some samples exhibiting a coexistence of both cluster structures. Although the clusters are monodisperse in size, structural diversity is apparent. Finally,more » the discovery of polymorphism may open up a new dimension in nanoscale engineering.« less

Probing the Initial Mass Function in Extended Ultraviolet (XUV) Disks

NASA Astrophysics Data System (ADS)

Koda, Jin

2013-01-01

"The GALEX UV satellite discovered tantalizing evidence of star formation (SF) far beyond the optical edge of galactic disks (i.e. extended UV disk, or XUV disk). This discovery provides a new opportunity for studying SF in the exceedingly low-density environment (˜1/10 of typical SF density), spurring intense debate on the universality of the initial mass function (IMF) in such exceptional environments. Our pilot S-Cam study of M83’s XUV disk led to support for the universal IMF at least in M83 (Koda et al. 2012). We propose an expansion of the pilot study by an order of magnitude, by observing additional 6 XUV disks in NA656(Hα), B, I, and R-band with S-Cam in S13A. In conjunction with GALEX UV bands, these images will reveal the presence of O stars (Hα; NA656-R) and O&B stars (UV) in stellar clusters -thus, constraining the high-mass end of the IMF. These multi-broadband images will enable us to determine the masses of the clusters with much improved accuracy (previously, relied only on R). The proposed observations will not only increase the statistical significance of our previous result, but also enable us to analyze the stochastic effect of IMF sampling in very low-mass - clusters (10^(2+3) M_sun) - the regime about which there is much ongoing debate."

Innovative Improvement and Intensification of Business Relationships Supported by Cooperative Networks

NASA Astrophysics Data System (ADS)

Vančová, Viera; Čambál, Miloš; Cagáňová, Dagmar

2012-12-01

Nowadays, the opportunity for companies to be involved in cluster initiatives and international business associations is a major factor that contributes to the increase of their innovative potential. Companies organized in technological clusters have greater access to mutual business contacts, faster information transfer and deployment of advanced technologies. These companies cooperate more frequently with universities and research - development institutions on innovative projects. An important benefit of cluster associations is that they create a suitable environment for innovation and the transfer of knowledge by means of international cooperation and networking. This supportive environment is not easy to access for different small and mediumsized companies, who are not members of any clusters or networks. Supplier-customer business channels expand by means of transnational networks and exchanges of experience. Knowledge potential is broadened and joint innovative projects are developed. Reflecting the growing importance of clusters as driving forces of economic and regional development, a number of cluster policies and initiatives have emerged in the last few decades, oriented to encourage the establishment of new clusters, to support existing clusters, or to assist the development of transnational cooperation. To achieve the goals of the Europe 2020 Strategy, European countries should have an interest in building strong clusters and developing cluster cooperation by sharing specialized research infrastructures and testing facilities and facilitating knowledge transfer for crossborder cooperation. This requires developing a long term joint strategy in order to facilitate the development of open global clusters and innovative small and medium entrepreneurs.

Detecting cancer clusters in a regional population with local cluster tests and Bayesian smoothing methods: a simulation study

PubMed Central

2013-01-01

Background There is a rising public and political demand for prospective cancer cluster monitoring. But there is little empirical evidence on the performance of established cluster detection tests under conditions of small and heterogeneous sample sizes and varying spatial scales, such as are the case for most existing population-based cancer registries. Therefore this simulation study aims to evaluate different cluster detection methods, implemented in the open soure environment R, in their ability to identify clusters of lung cancer using real-life data from an epidemiological cancer registry in Germany. Methods Risk surfaces were constructed with two different spatial cluster types, representing a relative risk of RR = 2.0 or of RR = 4.0, in relation to the overall background incidence of lung cancer, separately for men and women. Lung cancer cases were sampled from this risk surface as geocodes using an inhomogeneous Poisson process. The realisations of the cancer cases were analysed within small spatial (census tracts, N = 1983) and within aggregated large spatial scales (communities, N = 78). Subsequently, they were submitted to the cluster detection methods. The test accuracy for cluster location was determined in terms of detection rates (DR), false-positive (FP) rates and positive predictive values. The Bayesian smoothing models were evaluated using ROC curves. Results With moderate risk increase (RR = 2.0), local cluster tests showed better DR (for both spatial aggregation scales > 0.90) and lower FP rates (both < 0.05) than the Bayesian smoothing methods. When the cluster RR was raised four-fold, the local cluster tests showed better DR with lower FPs only for the small spatial scale. At a large spatial scale, the Bayesian smoothing methods, especially those implementing a spatial neighbourhood, showed a substantially lower FP rate than the cluster tests. However, the risk increases at this scale were mostly diluted by data aggregation. Conclusion High resolution spatial scales seem more appropriate as data base for cancer cluster testing and monitoring than the commonly used aggregated scales. We suggest the development of a two-stage approach that combines methods with high detection rates as a first-line screening with methods of higher predictive ability at the second stage. PMID:24314148

Is there a potential consumer market for low-sodium fermented sausages?

PubMed

Dos Santos, Bibiana A; Campagnol, Paulo C B; da Cruz, Adriano G; Morgano, Marcelo A; Wagner, Roger; Pollonio, Marise A R

2015-05-01

The NaCl levels in dry fermented sausages were reduced by 50% or were substituted with KCl, CaCl2 , or a blend of KCl and CaCl2 (1:1). The quality, safety, and the potential consumer market of dry fermented sausages were assessed. Neither 50% reduction of the NaCl content nor the substitution of 50% of the NaCl with KCl influenced the fermentation and maturation process. However, when CaCl2 was used as the substitute salt (50%), there was a significant decrease in pH, an increase in the water activity, and a decrease in lactic acid and micrococcus bacterial counts. Overall, the sensory acceptance decreased in dry fermented sausages with reduced sodium content. However, cluster analysis and internal preference mapping revealed potential for commercialization of samples with 50% of the NaCl content substituted with KCl or with a mixture of KCl and CaCl2 (1:1). © 2015 Institute of Food Technologists®

Conversion of Methane into Methanol and Ethanol over Nickel Oxide on Ceria-Zirconia Catalysts in a Single Reactor

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

Okolie, Chukwuemeka; Belhseine, Yasmeen F.; Lyu, Yimeng

Direct conversion of methane into alcohols is a promising technology for converting stranded methane reserves into liquids that can be transported in pipelines and upgraded to value-added chemicals. We demonstrate that a catalyst consisting of small nickel oxide clusters supported on ceria-zirconia (NiO/CZ) can selectively oxidize methane to methanol and ethanol in a single, steady-state process at 723 K using O2 as an abundantly available oxidant. The presence of steam is required to obtain alcohols rather than CO2 as the product of catalytic combustion. The unusual activity of this catalyst is attributed to the synergy between the small Lewis acidicmore » NiO clusters and the redox-active CZ support, which also stabilizes the small NiO clusters.« less

Conversion of Methane to Methanol and Ethanol over Nickel Oxide on Ceria-Zirconia Catalysts in a Single Reactor

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

Okolie, Chukwuemeka; Belhseine, Yasmeen F.; Lyu, Yimeng

Here, the conversion of methane into alcohols under moderate reaction conditions is a promising technology for converting stranded methane reserves into liquids that can be transported in pipelines and upgraded to value-added chemicals. We demonstrate that a catalyst consisting of small nickel oxide clusters supported on ceria-zirconia (NiO/CZ) can convert methane to methanol and ethanol in a single, steady-state process at 723 K using O 2 as an abundantly available oxidant. The presence of steam is required to obtain alcohols rather than CO 2 as the product of catalytic combustion. The unusual activity of this catalyst is attributed to themore » synergy between the small Lewis acidic NiO clusters and the redox-active CZ support, which also stabilizes the small NiO clusters.« less

Conversion of Methane to Methanol and Ethanol over Nickel Oxide on Ceria-Zirconia Catalysts in a Single Reactor

DOE PAGES

Okolie, Chukwuemeka; Belhseine, Yasmeen F.; Lyu, Yimeng; ...

2017-08-08

Here, the conversion of methane into alcohols under moderate reaction conditions is a promising technology for converting stranded methane reserves into liquids that can be transported in pipelines and upgraded to value-added chemicals. We demonstrate that a catalyst consisting of small nickel oxide clusters supported on ceria-zirconia (NiO/CZ) can convert methane to methanol and ethanol in a single, steady-state process at 723 K using O 2 as an abundantly available oxidant. The presence of steam is required to obtain alcohols rather than CO 2 as the product of catalytic combustion. The unusual activity of this catalyst is attributed to themore » synergy between the small Lewis acidic NiO clusters and the redox-active CZ support, which also stabilizes the small NiO clusters.« less

7 CFR 1780.9 - Eligible loan and grant purposes.

Code of Federal Regulations, 2010 CFR

2010-01-01

... installations or small clusters of users within an applicant's service area. The approval official should.... (5) Applicants providing service through individual or cluster facilities must obtain: (i) Easements...

Anesthesia for Euthanasia Influences mRNA Expression in Healthy Mice and after Traumatic Brain Injury

PubMed Central

Staib-Lasarzik, Irina; Kriege, Oliver; Timaru-Kast, Ralph; Pieter, Dana; Werner, Christian; Engelhard, Kristin

2014-01-01

Abstract Tissue sampling for gene expression analysis is usually performed under general anesthesia. Anesthetics are known to modulate hemodynamics, receptor-mediated signaling cascades, and outcome parameters. The present study determined the influence of anesthetic paradigms typically used for euthanization and tissue sampling on cerebral mRNA expression in mice. Naïve mice and animals with acute traumatic brain injury induced by controlled cortical impact (CCI) were randomized to the following euthanasia protocols (n=10–11/group): no anesthesia (NA), 1 min of 4 vol% isoflurane in room air (ISO), 3 min of a combination of 5 mg/kg midazolam, 0.05 mg/kg fentanyl, and 0.5 mg/kg medetomidine intraperitoneally (COMB), or 3 min of 360 mg/kg chloral hydrate intraperitoneally (CH). mRNA expression of actin-1-related gene (Act1), FBJ murine osteosarcoma viral oncogene homolog B (FosB), tumor necrosis factor alpha (TNFα), heat shock protein beta-1 (HspB1), interleukin (IL)-6, tight junction protein 1 (ZO-1), IL-1ß, cyclophilin A, micro RNA 497 (miR497), and small cajal body-specific RNA 17 were determined by real-time polymerase chain reaction (PCR) in hippocampus samples. In naïve animals, Act1 expression was downregulated in the CH group compared with NA. FosB expression was downregulated in COMB and CH groups compared with NA. CCI reduced Act1 and FosB expression, whereas HspB1 and TNFα expression increased. After CCI, HspB1 expression was significantly higher in ISO, COMB, and CH groups, and TNFα expression was elevated in ISO and COMB groups. MiR497, IL-6, and IL-1ß were upregulated after CCI but not affected by anesthetics. Effects were independent of absolute mRNA copy numbers. The data demonstrate that a few minutes of anesthesia before tissue sampling are sufficient to induce immediate mRNA changes, which seem to predominate in the early-regulated gene cluster. Anesthesia-related effects on gene expression might explain limited reproduciblity of real-time PCR data between studies or research groups and should therefore be considered for quantitative PCR data. PMID:24945082

Novel approach to classifying patients with pulmonary arterial hypertension using cluster analysis.

PubMed

Parikh, Kishan S; Rao, Youlan; Ahmad, Tariq; Shen, Kai; Felker, G Michael; Rajagopal, Sudarshan

2017-01-01

Pulmonary arterial hypertension (PAH) patients have distinct disease courses and responses to treatment, but current diagnostic and treatment schemes provide limited insight. We aimed to see if cluster analysis could distinguish clinical phenotypes in PAH. An unbiased cluster analysis was performed on 17 baseline clinical variables of PAH patients from the FREEDOM-M, FREEDOM-C, and FREEDOM-C2 randomized trials of oral treprostinil versus placebo. Participants were either treatment-naïve (FREEDOM-M) or on background therapy (FREEDOM-C, FREEDOM-C2). We tested for association of clusters with outcomes and interaction with respect to treatment. Primary outcome was 6-minute walking distance (6MWD) change. We included 966 participants with 12-week (FREEDOM-M) or 16-week (FREEDOM-C and FREEDOM-C2) follow-up. Four patient clusters were identified. Compared with Clusters 1 (n = 131) and 2 (n = 496), Clusters 3 (n = 246) and 4 (n = 93) patients were older, heavier, had worse baseline functional class, 6MWD, Borg Dyspnea Index, and fewer years since PAH diagnosis. Clusters also differed by PAH etiology and background therapies, but not gender or race. Mean treatment effect of oral treprostinil differed across Clusters 1-4 increased in a monotonic fashion (Cluster 1: 10.9 m; Cluster 2: 13.0 m; Cluster 3: 25.0 m; Cluster 4: 50.9 m; interaction P value = 0.048). We identified four distinct clusters of PAH patients based on common patient characteristics. Patients who were older, diagnosed with PAH for a shorter period, and had worse baseline symptoms and exercise capacity had the greatest response to oral treprostinil treatment.

Salt taste responses of the IXth nerve in Sprague-Dawley rats: lack of sensitivity to amiloride.

PubMed

Kitada, Y; Mitoh, Y; Hill, D L

1998-03-01

To explore characteristics of the salt taste function of taste receptor cells located on the posterior tongue, we recorded electrophysiological responses from the whole glossopharyngeal nerve in Sprague-Dawley (SD) rats. For all salts, relative response magnitudes increased with increased stimulus concentrations (0.2-2.0 M) of NH4+, K+, and Na+ salts. The order of effectiveness of stimulation for Cl- salts was NH4Cl > KCl > NaCl. For sodium salts, relative response magnitudes were anion dependent. Sodium salts with small anions (NaCl, NaSCN, and NaNO3) had a much stronger stimulating effect than sodium salts with large anion groups (Na2SO4, C2H3O2Na, and C6H11O7Na). The responses of the glossopharyngeal nerve to the Na+ salts of NaCl, C2H3O2Na, and C6H11O7Na were not inhibited by the lingual application of the epithelial sodium transport blocker amiloride. This is in contrast to large amiloride sensitivity of the chorda tympani nerve. Amiloride also failed to inhibit the responses to K+ salts (KCl and KC2H3O2) and to NH4Cl. These results demonstrate that taste receptors innervated by the glossopharyngeal nerve in SD rats lack amiloride sensitivity as observed in the glossopharyngeal nerve of spontaneously hypertensive and Wistar-Kyoto rats. Furthermore, the difference between the small-anion group and the large-anion group of Na+ salts in their effectiveness to produce responses in the glossopharyngeal nerve parallels the effects noted for the anion dependence in the portion of the taste response resistant to amiloride in the chorda tympani nerve. Sodium salts with the smaller anion produced the larger responses in both glossopharyngeal and chorda tympani nerves after amiloride.

Heterogeneity of the neuropeptide Y (NPY) contractile and relaxing receptors in horse penile small arteries.

PubMed

Prieto, Dolores; Arcos, Luis Rivera de Los; Martínez, Pilar; Benedito, Sara; García-Sacristán, Albino; Hernández, Medardo

2004-12-01

The distribution of neuropeptide Y (NPY)-immunorective nerves and the receptors involved in the effects of NPY upon electrical field stimulation (EFS)- and noradrenaline (NA)-elicited contractions were investigated in horse penile small arteries. NPY-immunoreactive nerves were widely distributed in the erectile tissues with a particularly high density around penile intracavernous small arteries. In small arteries isolated from the proximal part of the corpora cavernosa, NPY (30 nM) produced a variable modest enhancement of the contractions elicited by both EFS and NA. At the same concentration, the NPY Y(1) receptor agonist, [Leu(31), Pro(34)]NPY, markedly potentiated responses to EFS and NA, whereas the NPY Y(2) receptor agonist, NPY(13-36), enhanced exogenous NA-induced contractions. In arteries precontracted with NA, NPY, peptide YY (PYY), [Leu(31), Pro(34)]NPY and the NPY Y(2) receptor agonists, N-acetyl[Leu(28,31)]NPY (24-36) and NPY(13-36), elicited concentration-dependent contractile responses. Human pancreatic polypeptide (hPP) evoked a biphasic response consisting of a relaxation followed by contraction. NPY(3-36), the compound 1229U91 (Ile-Glu-Pro-Dapa-Tyr-Arg-Leu-Arg-Tyr-NH2, cyclic(2,4')diamide) and eventually NPY(13-36) relaxed penile small arteries. The selective NPY Y(1) receptor antagonist BIBP3226 ((R)-N(2)-(diphenacetyl)-N-[(4-hydroxyphenyl)methyl]D-arginineamide) (0.3 microM) shifted to the right the concentration-response curves to both NPY and [Leu(31), Pro(34)]NPY and inhibited the contractions induced by the highest concentrations of hPP but not the relaxations observed at lower doses. In the presence of the selective NPY Y(2) receptor antagonist BIIE0246 ((S)-N2-[[1-[2-[4-[(R,S)-5,11-dihydro-6(6h)-oxodibenz[b,e]azepin-11-y1]-1-piperazinyl]-2-oxoethyl]cyclo-pentyl-N-[2-[1,2-dihydro-3,5 (4H)-dioxo-1,2-diphenyl-3H-1,2, 4-triazol-4-yl]ethyl]-argininamide) (0.3 microM), the Y(2) receptor agonists NPY(13-36) and N-acetyl[Leu(28,31)]NPY (24-36) evoked potent slow relaxations in NA-precontracted arteries, under conditions of nitric oxide (NO) synthase blockade. Mechanical removal of the endothelium markedly enhanced contractions of NPY on NA-precontracted arteries, whereas blockade of the neuronal voltage-dependent Ca(2+) channels did not alter NPY responses. These results demonstrate that NPY can elicit dual contractile/relaxing responses in penile small arteries through a heterogeneous population of postjunctional NPY receptors. Potentiation of the contractions evoked by NA involve both NPY Y(1) and NPY Y(2) receptors. An NO-independent relaxation probably mediated by an atypical endothelial NPY receptor is also shown and unmasked in the presence of selective antagonists of the NPY contractile receptors.

Five ab initio potential energy and dipole moment surfaces for hydrated NaCl and NaF. I. Two-body interactions.

PubMed

Wang, Yimin; Bowman, Joel M; Kamarchik, Eugene

2016-03-21

We report full-dimensional, ab initio-based potentials and dipole moment surfaces for NaCl, NaF, Na(+)H2O, F(-)H2O, and Cl(-)H2O. The NaCl and NaF potentials are diabatic ones that dissociate to ions. These are obtained using spline fits to CCSD(T)/aug-cc-pV5Z energies. In addition, non-linear least square fits using the Born-Mayer-Huggins potential are presented, providing accurate parameters based strictly on the current ab initio energies. The long-range behavior of the NaCl and NaF potentials is shown to go, as expected, accurately to the point-charge Coulomb interaction. The three ion-H2O potentials are permutationally invariant fits to roughly 20,000 coupled cluster CCSD(T) energies (awCVTZ basis for Na(+) and aVTZ basis for Cl(-) and F(-)), over a large range of distances and H2O intramolecular configurations. These potentials are switched accurately in the long range to the analytical ion-dipole interactions, to improve computational efficiency. Dipole moment surfaces are fits to MP2 data; for the ion-ion cases, these are well described in the intermediate- and long-range by the simple point-charge expression. The performance of these new fits is examined by direct comparison to additional ab initio energies and dipole moments along various cuts. Equilibrium structures, harmonic frequencies, and electronic dissociation energies are also reported and compared to direct ab initio results. These indicate the high fidelity of the new PESs.

Crystalline embryos at ice-vapor interfaces

NASA Technical Reports Server (NTRS)

Bartley, D. L.

1976-01-01

The nucleation of small monolayer ice-like clusters at the basal and prism ice-vapor interfaces is considered. It is found that the basal surfaces prefer triangular embryos with an orientation that reverses from layer to layer, whereas the most stable clusters on the prism surfaces are rectangular in configuration. At any given saturation ratio, the preferred prism clusters are found to have a critical energy of formation significantly lower than that of the basal clusters, basically because of differences in cluster corner free energies.

Multivariate analysis of selected metals in tannery effluents and related soil.

PubMed

Tariq, Saadia R; Shah, Munir H; Shaheen, N; Khalique, A; Manzoor, S; Jaffar, M

2005-06-30

Effluent and relevant soil samples from 38 tanning units housed in Kasur, Pakistan, were obtained for metal analysis by flame atomic absorption spectrophotometric method. The levels of 12 metals, Na, Ca, K, Mg, Fe, Mn, Cr, Co, Cd, Ni, Pb and Zn were determined in the two media. The data were evaluated towards metal distribution and metal-to-metal correlations. The study evidenced enhanced levels of Cr (391, 16.7 mg/L) and Na (25,519, 9369 mg/L) in tannery effluents and relevant soil samples, respectively. The effluent versus soil trace metal content relationship confirmed that the effluent Cr was strongly correlated with soil Cr. For metal source identification the techniques of principal component analysis, and cluster analysis were applied. The principal component analysis yielded two factors for effluents: factor 1 (49.6% variance) showed significant loading for Ca, Fe, Mn, Cr, Cd, Ni, Pb and Zn, referring to a tanning related source for these metals, and factor 2 (12.6% variance) with higher loadings of Na, K, Mg and Co, was associated with the processes during the skin/hide treatment. Similarly, two factors with a cumulative variance of 34.8% were obtained for soil samples: factor 1 manifested the contribution from Mg, Mn, Co, Cd, Ni and Pb, which though soil-based is basically effluent-derived, while factor 2 was found associated with Na, K, Ca, Cr and Zn which referred to a tannery-based source. The dendograms obtained from cluster analysis, also support the observed results. The study exhibits a gross pollution of soils with Cr at levels far exceeding the stipulated safe limit laid down for tannery effluents.

Comparative study of energy of particles ejected from coulomb explosion of rare gas and metallic clusters irradiated by intense femtosecond laser field

NASA Astrophysics Data System (ADS)

Boucerredj, N.; Beggas, K.

2016-10-01

We present our study of high intensity femtosecond laser field interaction with large cluster of Kr and Na (contained 2.103 to 2.107 atoms). When laser intensity is above a critical value, it blows off all of electrons from the cluster and forms a non neutral ion cloud. The irradiation of these clusters by the intense laser field leads to highly excitation energy which can be the source of energetic electrons, electronic emission, highly charge, energetic ions and fragmentation process. During the Coulomb explosion of the resulting highly ionized, high temperature nanoplasma, ions acquire again their energy. It is shown that ultra fast ions are produced. The goal of our study is to investigate in detail a comparative study of the expansion and explosion then the ion energy of metallic and rare gas clusters irradiated by an intense femtosecond laser field. We have found that ions have a kinetic energy up to 105 eV and the Coulomb pressure is little than the hydrodynamic pressure. The Coulomb explosion of a cluster may provide a new high energy ion source.

Abundances in the Young Globulars Ruprecht 106 and PAL 12

NASA Astrophysics Data System (ADS)

Brown, J. A.; Wallerstein, G.; Zucker, D.

1995-12-01

We have observed two red giants in each of the young globular clusters Ruprecht 106 and Pal 12 with the CTIO 4m echelle and analyzed the spectra for chemical composition. We find for Rup 106 [Fe/H] =~ -1.5, [O/Fe] =~ 0.0, and [alpha /Fe] =~ -0.2. For Pal 12 we find [Fe/H] =~ -1.0 and [alpha /Fe] =~ -0.05; we have no information on oxygen in Pal 12. The light odd-Z metals Na and Al are both overdeficient in both clusters' stars. The stars are all CN-weak compared to similar giants in nearby globulars of comparable [Fe/H]. The abundance results for Rup 106 rule out the possibility that the apparent youth of the cluster as derived from its color-magnitude diagram is caused by an anomalous composition; the lack of results for oxygen prevent us from making a similar statement for Pal 12. These abundances imply a very different star formation history for the material from which these clusters formed, compared to the well-studied old nearby globulars, and are consistent with the suggestion that these clusters are accreted objects, and were not formed in the same environment as the old clusters.

Towards Accurate Modelling of Galaxy Clustering on Small Scales: Testing the Standard ΛCDM + Halo Model

NASA Astrophysics Data System (ADS)

Sinha, Manodeep; Berlind, Andreas A.; McBride, Cameron K.; Scoccimarro, Roman; Piscionere, Jennifer A.; Wibking, Benjamin D.

2018-04-01

Interpreting the small-scale clustering of galaxies with halo models can elucidate the connection between galaxies and dark matter halos. Unfortunately, the modelling is typically not sufficiently accurate for ruling out models statistically. It is thus difficult to use the information encoded in small scales to test cosmological models or probe subtle features of the galaxy-halo connection. In this paper, we attempt to push halo modelling into the "accurate" regime with a fully numerical mock-based methodology and careful treatment of statistical and systematic errors. With our forward-modelling approach, we can incorporate clustering statistics beyond the traditional two-point statistics. We use this modelling methodology to test the standard ΛCDM + halo model against the clustering of SDSS DR7 galaxies. Specifically, we use the projected correlation function, group multiplicity function and galaxy number density as constraints. We find that while the model fits each statistic separately, it struggles to fit them simultaneously. Adding group statistics leads to a more stringent test of the model and significantly tighter constraints on model parameters. We explore the impact of varying the adopted halo definition and cosmological model and find that changing the cosmology makes a significant difference. The most successful model we tried (Planck cosmology with Mvir halos) matches the clustering of low luminosity galaxies, but exhibits a 2.3σ tension with the clustering of luminous galaxies, thus providing evidence that the "standard" halo model needs to be extended. This work opens the door to adding interesting freedom to the halo model and including additional clustering statistics as constraints.

Inherent size effects on XANES of nanometer metal clusters: Size-selected platinum clusters on silica

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

Dai, Yang; Gorey, Timothy J.; Anderson, Scott L.

2016-12-12

X-ray absorption near-edge structure (XANES) is commonly used to probe the oxidation state of metal-containing nanomaterials, however, as the particle size in the material drops below a few nanometers, it becomes important to consider inherent size effects on the electronic structure of the materials. In this paper, we analyze a series of size-selected Pt n/SiO 2 samples, using X-ray photoelectron spectroscopy (XPS), low energy ion scattering, grazing-incidence small angle X-ray scattering, and XANES. The oxidation state and morphology are characterized both as-deposited in UHV, and after air/O 2 exposure and annealing in H 2. Here, the clusters are found tomore » be stable during deposition and upon air exposure, but sinter if heated above ~150 °C. XANES shows shifts in the Pt L 3 edge, relative to bulk Pt, that increase with decreasing cluster size, and the cluster samples show high white line intensity. Reference to bulk standards would suggest that the clusters are oxidized, however, XPS shows that they are not. Instead, the XANES effects are attributable to development of a band gap and localization of empty state wavefunctions in small clusters.« less

Ultra-small Ag clusters in zeolite A4: Antibacterial and thermochromic applications

NASA Astrophysics Data System (ADS)

Horta-Fraijo, P.; Cortez-Valadez, M.; Flores-Lopez, N. S.; Britto Hurtado, R.; Vargas-Ortiz, R. A.; Perez-Rodriguez, A.; Flores-Acosta, M.

2018-03-01

The physical and chemical properties of metal clusters depend on their atomic structure, therefore, it is important to determine the lowest-energy structures of the clusters in order to understand and utilize their properties. In this work, we use the Density Functional Theory (DFT) at the generalized gradient approximation level Becke's three-parameter and the gradient corrected functional of Lee, Yang and Puar (B3LYP) in combination with the basis set LANL2DZ (the effective core potentials and associated double-zeta valence) to determine some of the structural, electronic and vibrational properties of the planar silver clusters (Agn clusters n = 2-24). Additionally, the study reports the experimental synthesis of small silver clusters in synthetic zeolite A4. The synthesis was possible using the ion exchange method with some precursors like silver nitrate (AgNO3) and synthetic zeolite A4. The silver clusters in zeolite powder underwent thermal treatment at 450 °C to release the remaining water or humidity on it. The morphology of the particles was determined by Transmission Electron microscopy. The nanomaterials obtained show thermochromic properties. The structural parameters were correlated theoretically and experimentally.

Structure and orientation of small particles of platinum deposited on NaCl and mica

NASA Technical Reports Server (NTRS)

Renou, A.; Gillet, M.

1979-01-01

The structure of small platinum particles condensed in vacuum onto NaCl (001), NaCl (111) and mica substrates was studied by electron diffraction and electron microscopy. Results show that above a certain substrate temperature decahedral or icosahedral particles are formed. These particles are practically absent with substrates cleaved in high vacuum. They are always much less numerous than in gold films prepared under the same conditions. Assumptions made to explain this phenomenon are: (1) the initial growth of an abnormal structure of the nuclei as opposed by the substrate; (2) the particles disappear before they attain a size which corresponds to the observations; and (3) the particles result from a coalescence mechanism leading to multiple twinned particles.

Controlled clustering of carboxylated SPIONs through polyethylenimine

NASA Astrophysics Data System (ADS)

Nesztor, Dániel; Bali, Krisztina; Tóth, Ildikó Y.; Szekeres, Márta; Tombácz, Etelka

2015-04-01

Clusters of magnetite nanoparticles (MNPs) were synthesized using poly(acrylic acid-co-maleic acid) coated MNPs (PAM@MNP) and branched polyethylenimine (PEI). Materials were characterized by potentiometric titration, zeta potential and dynamic light scattering (DLS) measurements. PEI and PAM@MNP are oppositely charged as characterized by zeta potential measurements (+8, -34 mV respectively) and titration (10.30 mmol -NH3+/g PEI; 0.175 mmol -COO-/g PAM@MNP) at pH 6.5±0.2; therefore magnetic clusters are formed by electrostatic adhesion. Two different preparation methods and the effect of PEI and electrolyte (NaCl) concentration on the cluster formation was studied. Choosing an optimal concentration of PEI (charge ratio of PEI to PAM@MNP: 0.17) and electrolyte (10 mM), a concentrated (10 g MNP/L) product containing PEI-PAM@MNP nanoclusters with size of 165±10 nm was prepared. Its specific absorption rate (SAR) measured in AC magnetic field (110 kHz, 25 mT) is 12 W/g Fe. The clustered product is expected to have enhanced contrast efficiency in MRI.

Developing cluster strategy of apples dodol SMEs by integration K-means clustering and analytical hierarchy process method

NASA Astrophysics Data System (ADS)

Mustaniroh, S. A.; Effendi, U.; Silalahi, R. L. R.; Sari, T.; Ala, M.

2018-03-01

The purposes of this research were to determine the grouping of apples dodol small and medium enterprises (SMEs) in Batu City and to determine an appropriate development strategy for each cluster. The methods used for clustering SMEs was k-means. The Analytical Hierarchy Process (AHP) approach was then applied to determine the development strategy priority for each cluster. The variables used in grouping include production capacity per month, length of operation, investment value, average sales revenue per month, amount of SMEs assets, and the number of workers. Several factors were considered in AHP include industry cluster, government, as well as related and supporting industries. Data was collected using the methods of questionaire and interviews. SMEs respondents were selected among SMEs appels dodol in Batu City using purposive sampling. The result showed that two clusters were formed from five apples dodol SMEs. The 1stcluster of apples dodol SMEs, classified as small enterprises, included SME A, SME C, and SME D. The 2ndcluster of SMEs apples dodol, classified as medium enterprises, consisted of SME B and SME E. The AHP results indicated that the priority development strategy for the 1stcluster of apples dodol SMEs was improving quality and the product standardisation, while for the 2nd cluster was increasing the marketing access.

CA II TRIPLET SPECTROSCOPY OF SMALL MAGELLANIC CLOUD RED GIANTS. III. ABUNDANCES AND VELOCITIES FOR A SAMPLE OF 14 CLUSTERS

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

Parisi, M. C.; Clariá, J. J.; Marcionni, N.

2015-05-15

We obtained spectra of red giants in 15 Small Magellanic Cloud (SMC) clusters in the region of the Ca ii lines with FORS2 on the Very Large Telescope. We determined the mean metallicity and radial velocity with mean errors of 0.05 dex and 2.6 km s{sup −1}, respectively, from a mean of 6.5 members per cluster. One cluster (B113) was too young for a reliable metallicity determination and was excluded from the sample. We combined the sample studied here with 15 clusters previously studied by us using the same technique, and with 7 clusters whose metallicities determined by other authorsmore » are on a scale similar to ours. This compilation of 36 clusters is the largest SMC cluster sample currently available with accurate and homogeneously determined metallicities. We found a high probability that the metallicity distribution is bimodal, with potential peaks at −1.1 and −0.8 dex. Our data show no strong evidence of a metallicity gradient in the SMC clusters, somewhat at odds with recent evidence from Ca ii triplet spectra of a large sample of field stars. This may be revealing possible differences in the chemical history of clusters and field stars. Our clusters show a significant dispersion of metallicities, whatever age is considered, which could be reflecting the lack of a unique age–metallicity relation in this galaxy. None of the chemical evolution models currently available in the literature satisfactorily represents the global chemical enrichment processes of SMC clusters.« less

Expression patterns of WRKY genes in di-haploid Populus simonii × P. nigra in response to salinity stress revealed by quantitative real-time PCR and RNA sequencing.

PubMed

Wang, Shengji; Wang, Jiying; Yao, Wenjing; Zhou, Boru; Li, Renhua; Jiang, Tingbo

2014-10-01

Spatio-temporal expression patterns of 13 out of 119 poplar WRKY genes indicated dynamic and tissue-specific roles of WRKY family proteins in salinity stress tolerance. To understand the expression patterns of poplar WRKY genes under salinity stress, 51 of the 119 WRKY genes were selected from di-haploid Populus simonii × P. nigra by quantitative real-time PCR (qRT-PCR). We used qRT-PCR to profile the expression of the top 13 genes under salinity stress across seven time points, and employed RNA-Seq platforms to cross-validate it. Results demonstrated that all the 13 WRKY genes were expressed in root, stem, and leaf tissues, but their expression levels and overall patterns varied notably in these tissues. Regarding overall gene expression in roots, the 13 genes were significantly highly expressed at all six time points after the treatment, reaching the plateau of expression at hour 9. In leaves, the 13 genes were similarly up-regulated from 3 to 12 h in response to NaCl treatment. In stems, however, expression levels of the 13 genes did not show significant changes after the NaCl treatment. Regarding individual gene expression across the time points and the three tissues, the 13 genes can be classified into three clusters: the lowly expressed Cluster 1 containing PthWRKY28, 45 and 105; intermediately expressed Clusters 2 including PthWRKY56, 88 and 116; and highly expressed Cluster 3 consisting of PthWRKY41, 44, 51, 61, 62, 75 and 106. In general, genes in Cluster 2 and 3 displayed a dynamic pattern of "induced amplification-recovering", suggesting that these WRKY genes and corresponding pathways may play a critical role in mediating salt response and tolerance in a dynamic and tissue-specific manner.

Hydrogeochemistry and water quality of the Kordkandi-Duzduzan plain, NW Iran: application of multivariate statistical analysis and PoS index.

PubMed

Soltani, Shahla; Asghari Moghaddam, Asghar; Barzegar, Rahim; Kazemian, Naeimeh; Tziritis, Evangelos

2017-08-18

Kordkandi-Duzduzan plain is one of the fertile plains of East Azarbaijan Province, NW of Iran. Groundwater is an important resource for drinking and agricultural purposes due to the lack of surface water resources in the region. The main objectives of the present study are to identify the hydrogeochemical processes and the potential sources of major, minor, and trace metals and metalloids such as Cr, Mn, Cd, Fe, Al, and As by using joint hydrogeochemical techniques and multivariate statistical analysis and to evaluate groundwater quality deterioration with the use of PoS environmental index. To achieve these objectives, 23 groundwater samples were collected in September 2015. Piper diagram shows that the mixed Ca-Mg-Cl is the dominant groundwater type, and some of the samples have Ca-HCO 3 , Ca-Cl, and Na-Cl types. Multivariate statistical analyses indicate that weathering and dissolution of different rocks and minerals, e.g., silicates, gypsum, and halite, ion exchange, and agricultural activities influence the hydrogeochemistry of the study area. The cluster analysis divides the samples into two distinct clusters which are completely different in EC (and its dependent variables such as Na + , K + , Ca 2+ , Mg 2+ , SO 4 2- , and Cl - ), Cd, and Cr variables according to the ANOVA statistical test. Based on the median values, the concentrations of pH, NO 3 - , SiO 2 , and As in cluster 1 are elevated compared with those of cluster 2, while their maximum values occur in cluster 2. According to the PoS index, the dominant parameter that controls quality deterioration is As, with 60% of contribution. Samples of lowest PoS values are located in the southern and northern parts (recharge area) while samples of the highest values are located in the discharge area and the eastern part.

Dependence of the clustering properties of galaxies on stellar velocity dispersion in the Main galaxy sample of SDSS DR10

NASA Astrophysics Data System (ADS)

Deng, Xin-Fa; Song, Jun; Chen, Yi-Qing; Jiang, Peng; Ding, Ying-Ping

2014-08-01

Using two volume-limited Main galaxy samples of the Sloan Digital Sky Survey Data Release 10 (SDSS DR10), we investigate the dependence of the clustering properties of galaxies on stellar velocity dispersion by cluster analysis. It is found that in the luminous volume-limited Main galaxy sample, except at r=1.2, richer and larger systems can be more easily formed in the large stellar velocity dispersion subsample, while in the faint volume-limited Main galaxy sample, at r≥0.9, an opposite trend is observed. According to statistical analyses of the multiplicity functions, we conclude in two volume-limited Main galaxy samples: small stellar velocity dispersion galaxies preferentially form isolated galaxies, close pairs and small group, while large stellar velocity dispersion galaxies preferentially inhabit the dense groups and clusters. However, we note the difference between two volume-limited Main galaxy samples: in the faint volume-limited Main galaxy sample, at r≥0.9, the small stellar velocity dispersion subsample has a higher proportion of galaxies in superclusters ( n≥200) than the large stellar velocity dispersion subsample.

The fate of NGC602, an intense region of star-formation in the Wing of the SMC

NASA Astrophysics Data System (ADS)

Sabbi, Elena

2017-08-01

This is a small 2 orbit proposal designed to measure the internal dynamics of NGC602, a small region of intense star formation in the Wing of the SMC, with a low gas and dust density that has been often considered an unfavorable place for star formation. Small regions of massive star formation are important to study for our understanding of the process of star and cluster formation, the ionization of the interstellar medium, and the injection of energy and momentum into their host galaxy. By combining our new observations with archival ACS/WFC data acquired in July 2004, we will be able to measure the relative proper motions of the NGC602 sub-structures better than 2.3 km/s and investigate the nature of the apparently isolated massive stars found around NGC602. This study will provide unique observational data to characterize the early phase of cluster evolution and test cluster formation theories. It will also address significant open issues in star formation, cluster dynamics and the origin of isolated supernovae and GRBs.

The Cool Stellar Populations of Early-Type Galaxies and the Galactic Bulge

NASA Astrophysics Data System (ADS)

Houdashelt, Mark Lee

1995-01-01

Red (6800-9200 A) and near-infrared (K-band) spectra have been obtained for 34 early-type galaxies in the Virgo cluster, the Coma cluster and the field. The strengths of the Ca II triplet (lambdalambda 8498, 8542, 8662 A), the Na I doublet ( lambdalambda8183, 8195 A), the Mg I lambda8807 A line, and molecular bands of TiO and VO were measured from the red spectra. Absorption due to the CO band with bandhead at 2.29 mu m was measured from the near-infrared spectra. The behavior of the spectral indices was examined for the Virgo galaxy nuclei as functions of luminosity and color. Overall, the CO, TiO and Na I indices were found to be stronger in redder and brighter galaxies. The Mg I and the Ca II triplet lines did not vary significantly among galaxies of different color or brightness. These trends are consistent with a change in chemical composition producing the well-known color-magnitude relation for early -type galaxies. No significant differences were detected among galaxies of similar luminosity in the Virgo cluster, the Coma cluster and the field. To simulate the stellar population changes implied by the radial color gradients observed in early-type galaxies, models were constructed to represent the integrated light of the Galactic bulge as a function of latitude. A field in Baade's Window (BW) was studied first and the stellar population there was found to be quite inhomogeneous. The BW model indicated that the integrated light of BW is giant -dominated, and the BW spectral energy distribution is very similar to that of the nucleus of a low-luminosity early -type galaxy. From models of BW and a field at b = -8^circ, radial gradients were estimated for the Galactic bulge and compared to the changes which occur along a luminosity sequence of early -type galaxies in the Virgo cluster. This comparison showed that: (1) the Na I and I(8197) indices increase steeply with redder colors in the Virgo galaxies but appear to decrease with color in the Galactic bulge; this effect is not understood but may be caused by some deficiency in the modelling; and (2) differences in the slopes of the TiO-color trends in E/S0 galaxies and in the Galactic bulge may indicate that the (Ti/Fe) ratio is changing differently in these two instances.

The Organization of Children's Same-Sex Peer Relationships.

ERIC Educational Resources Information Center

Benenson, Joyce; Apostoleris, Nicholas; Parnass, Jodi

1998-01-01

Uses a sociometric analysis to explore the differential organization of boys' and girls' peer groups. Finds that boys structure their peer groups by creating a large central cluster composed of smaller integrated clusters, whereas girls form small clusters unrelated to one another. Nevertheless, girls are aware of and sensitive to the status of…

The Giant Branch of omega Centauri. IV. Abundance Patterns Based on Echelle Spectra of 40 Red Giants

NASA Astrophysics Data System (ADS)

Norris, John E.; Da Costa, G. S.

1995-07-01

Abundances of some 20 elements have been determined for a (biased) sample of 40 red giants having Mv < -1.5 in the chemically inhomogeneous globular cluster ω Centauri. The results are based on high-resolution, high signal-to-noise echelle spectra and permit one to examine the roles of primordial enrichment and stellar evolutionary mixing effects in the cluster. Our basic conclusions are as follows (1) There is an abundance range -1.8 < [Fe/H] < -0.8, and even more metal rich stars may exist in the cluster. (2) For the α (Mg, Si, Ca, Ti) and iron peak (Cr, Ni) elements and Sc and V, [metal/Fe] is flat as a function of [Fe/H] and is consistent with primordial enrichment from stars having mass greater than 10 Msun, as has been found for field halo stars. (3) There is a large scatter in the abundances of C, N, and 0. The bulk of the stars have -0.9 < [C/Fe] < -0.3 and [O/Fe] ˜ 0.3, as is found at the red giant branch tip in other "normal" (showing no spread in [Fe/H]) clusters of similar abundance, while there also exists a group of CN-strong stars having [C/Fe] ˜ -0.7 and [O/Fe] ˜ -0.5. Nitrogen appears to be enhanced in all of these carbon-depleted stars. These results are most readily explained in terms of evolutionary mixing effects not predicted by standard stellar evolution calculations and are consistent with the earlier suggestions of Cohen & Bell (1986) and Paltoglou & Norris (1989) concerning processing in both the CN and ON cycles in the stars being observed. In contrast, the group of CO-strong stars first identified by Persson et al. (1980) has [C/Fe] ˜ 0.0, [O/Fe] ˜ 0.4, and [N/Fe] ˜ 0.4 (or 0.9 if the nitrogen scale of Brown and Wallerstein is correct) and is suggestive of primordial enrichment of carbon and/or nitrogen from intermediate- and possibly low-mass stars, tempered by later stellar evolutionary effects. (4) [Na/Fe] and [Al/Fe] are anticorrelated with [O/Fe], and there is a positive correlation between [Na/Fe] and [Al/Fe], all of which are most readily explained in terms of evolutionary mixing effects as first suggested by Denisenkov & Denisenkova (1990). Such an explanation is supported by the similar ([Na/Fe], [O/Fe]) anticorrelation reported by Kraft et al. (1993) in the "normal" globular clusters. (5) For the heavy neutron-addition elements (in particular Y, Ba, La, and Nd) [heavy metal/Fe] rises as [Fe/H] increases, in sharp contrast with what is found in the "normal" clusters, while the relative abundances as a function of atomic number are suggestive of s-processing. The increase in [heavy metal/Fe] with [Fe/H] appears independent of the abundance of C, N, O, Na and Al and is most naturally explained as a primordial effect. Guided by the predictions of existing (somewhat uncertain) stellar evolution calculations, we suggest that this results from primordial enrichment from stars having mass as low as 1-3 Msun. (6) If the preceding suggestion is correct, chemical enrichment in ω Cen occurred over an extended period, perhaps ≥1 Gyr.

Excretion of NaCl and KCl loads in mosquitoes. 2. Effects of the small molecule Kir channel modulator VU573 and its inactive analog VU342

PubMed Central

Rouhier, Matthew F.; Hine, Rebecca M.; Park, Seokhwan Terry; Raphemot, Rene; Denton, Jerod; Piermarini, Peter M.

2014-01-01

The effect of two small molecules VU342 and VU573 on renal functions in the yellow fever mosquito Aedes aegypti was investigated in vitro and in vivo. In isolated Malpighian tubules, VU342 (10 μM) had no effect on the transepithelial secretion of Na+, K+, Cl−, and water. In contrast, 10 μM VU573 first stimulated and then inhibited the transepithelial secretion of fluid when the tubules were bathed in Na+-rich or K+-rich Ringer solution. The early stimulation was blocked by bumetanide, suggesting the transient stimulation of Na-K-2Cl cotransport, and the late inhibition of fluid secretion was consistent with the known block of AeKir1, an Aedes inward rectifier K+ channel, by VU573. VU342 and VU573 at a hemolymph concentration of about 11 μM had no effect on the diuresis triggered by hemolymph Na+ or K+ loads. VU342 at a hemolymph concentration of 420 μM had no effect on the diuresis elicited by hemolymph Na+ or K+ loads. In contrast, the same concentration of VU573 significantly diminished the Na+ diuresis by inhibiting the urinary excretion of Na+, Cl−, and water. In K+-loaded mosquitoes, 420 μM VU573 significantly diminished the K+ diuresis by inhibiting the urinary excretion of K+, Na+, Cl−, and water. We conclude that 1) the effects of VU573 observed in isolated Malpighian tubules are overwhelmed in vivo by the diuresis triggered with the coinjection of Na+ and K+ loads, and 2) at a hemolymph concentration of 420 μM VU573 affects Kir channels systemically, including those that might be involved in the release of diuretic hormones. PMID:25056106

Anger Problem Profiles among Partner Violent Men: Differences in Clinical Presentation and Treatment Outcome

ERIC Educational Resources Information Center

Murphy, Christopher M.; Taft, Casey T.; Eckhardt, Christopher I.

2007-01-01

Cluster analysis of 139 partner violent men's self-reports on the State-Trait Anger Expression Inventory identified profiles reflecting pathological anger (PA), low anger control (LAC), and normal anger (NA). The PA group self-reported higher pretreatment partner abuse, interpersonal dysfunction, distress, and substance abuse and had lower…

Evolution of the properties of Al(n)N(n) clusters with size.

PubMed

Costales, Aurora; Blanco, M A; Francisco, E; Pandey, Ravindra; Martín Pendás, A

2005-12-29

A global optimization of stoichiometric (AlN)(n) clusters (n = 1-25, 30, 35, ..., 95, 100) has been performed using the basin-hopping (BH) method and describing the interactions with simple and yet realistic interatomic potentials. The results for the smaller isomers agree with those of previous electronic structure calculations, thus validating the present scheme. The lowest-energy isomers found can be classified in three different categories according to their structural motifs: (i) small clusters (n = 2-5), with planar ring structures and 2-fold coordination, (ii) medium clusters (n = 6-40), where a competition between stacked rings and globular-like empty cages exists, and (iii) large clusters (n > 40), large enough to mix different elements of the previous stage. All the atoms in small and medium-sized clusters are in the surface, while large clusters start to display interior atoms. Large clusters display a competition between tetrahedral and octahedral-like features: the former lead to a lower energy interior in the cluster, while the latter allow for surface terminations with a lower energy. All of the properties studied present different regimes according to the above classification. It is of particular interest that the local properties of the interior atoms do converge to the bulk limit. The isomers with n = 6 and 12 are specially stable with respect to the gain or loss of AlN molecules.

Chemical Complexity in the Eu-enhanced Monometallic Globular NGC 5986

NASA Astrophysics Data System (ADS)

Johnson, Christian I.; Caldwell, Nelson; Rich, R. Michael; Mateo, Mario; Bailey, John I., III; Olszewski, Edward W.; Walker, Matthew G.

2017-06-01

NGC 5986 is a poorly studied but relatively massive Galactic globular cluster that shares several physical and morphological characteristics with “iron-complex” clusters known to exhibit significant metallicity and heavy-element dispersions. In order to determine whether NGC 5986 joins the iron-complex cluster class, we investigated the chemical composition of 25 red giant branch and asymptotic giant branch cluster stars using high-resolution spectra obtained with the Magellan-M2FS instrument. Cluster membership was verified using a combination of radial velocity and [Fe/H] measurements, and we found the cluster to have a mean heliocentric radial velocity of +99.76 km s-1 (σ = 7.44 km s-1). We derived a mean metallicity of [Fe/H] = -1.54 dex (σ = 0.08 dex), but the cluster’s small dispersion in [Fe/H] and low [La/Eu] abundance preclude it from being an iron-complex cluster. NGC 5986 has < [{Eu}/{Fe}]> =+0.76 {dex} (σ = 0.08 dex), which is among the highest ratios detected in a Galactic cluster, but the small [Eu/Fe] dispersion is puzzling because such high values near [Fe/H] ˜ -1.5 are typically only found in dwarf galaxies exhibiting large [Eu/Fe] variations. NGC 5986 exhibits classical globular cluster characteristics, such as uniformly enhanced [α/Fe] ratios, a small dispersion in Fe-peak abundances, and (anti)correlated light-element variations. Similar to NGC 2808, we find evidence that NGC 5986 may host at least four to five populations with distinct light-element compositions, and the presence of a clear Mg-Al anticorrelation along with an Al-Si correlation suggests that the cluster gas experienced processing at temperatures ≳65-70 MK. However, the current data do not support burning temperatures exceeding ˜100 MK. We find some evidence that the first- and second-generation stars in NGC 5986 may be fully spatially mixed, which could indicate that the cluster has lost a significant fraction of its original mass. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Detailed chemical abundance analysis of the thick disk star cluster Gaia 1

NASA Astrophysics Data System (ADS)

Koch, Andreas; Hansen, Terese T.; Kunder, Andrea

2018-01-01

Star clusters, particularly those objects in the disk-bulge-halo interface are as yet poorly charted, despite the fact that they carry important information about the formation and the structure of the Milky Way. Here, we present a detailed chemical abundance study of the recently discovered object Gaia 1. Photometry has previously suggested it as an intermediate-age, moderately metal-rich system, although the exact values for its age and metallicity remained ambiguous in the literature. We measured detailed chemical abundances of 14 elements in four red giant members, from high-resolution (R = 25 000) spectra that firmly establish Gaia 1 as an object associated with the thick disk. The resulting mean Fe abundance is -0.62 ± 0.03(stat.)± 0.10(sys.) dex, which is more metal-poor than indicated by previous spectroscopy from the literature, but it is fully in line with values from isochrone fitting. We find that Gaia 1 is moderately enhanced in the α-elements, which allowed us to consolidate its membership with the thick disk via chemical tagging. The cluster's Fe-peak and neutron-capture elements are similar to those found across the metal-rich disks, where the latter indicate some level of s-process activity. No significant spread in iron nor in other heavy elements was detected, whereas we find evidence of light-element variations in Na, Mg, and Al. Nonetheless, the traditional Na-O and Mg-Al (anti-)correlations, typically seen in old globular clusters, are not seen in our data. This confirms that Gaia 1 is rather a massive and luminous open cluster than a low-mass globular cluster. Finally, orbital computations of the target stars bolster our chemical findings of Gaia 1's present-day membership with the thick disk, even though it remains unclear which mechanisms put it in that place. This paper includes data gathered with the 2.5 meter du Pont Telescope located at Las Campanas Observatory, Chile.Full Table 2 is 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/609/A13

Major signal suppression from metal ion clusters in SFC/ESI-MS - Cause and effects.

PubMed

Haglind, Alfred; Hedeland, Mikael; Arvidsson, Torbjörn; Pettersson, Curt E

2018-05-01

The widening application area of SFC-MS with polar analytes and water-containing samples facilitates the use of quick and simple sample preparation techniques such as "dilute and shoot" and protein precipitation. This has also introduced new polar interfering components such as alkali metal ions naturally abundant in e.g. blood plasma and urine, which have shown to be retained using screening conditions in SFC/ESI-TOF-MS and causing areas of major ion suppression. Analytes co-eluting with these clusters will have a decreased signal intensity, which might have a major effect on both quantification and identification. When investigating the composition of the alkali metal clusters using accurate mass and isotopic pattern, it could be concluded that they were previously not described in the literature. Using NaCl and KCl standards and different chromatographic conditions, varying e.g. column and modifier, the clusters proved to be formed from the alkali metal ions in combination with the alcohol modifier and make-up solvent. Their compositions were [(XOCH 3 ) n  + X] + , [(XOH) n  + X] + , [(X 2 CO 3 ) n  + X] + and [(XOOCOCH 3 ) n  + X] + for X = Na + or K + in ESI+. In ESI-, the clusters depended more on modifier, with [(XCl) n  + Cl] - and [(XOCH 3 ) n  + OCH 3 ] - mainly formed in pure methanol and [(XOOCH) n  + OOCH] - when 20 mM NH 4 Fa was added. To prevent the formation of the clusters by avoiding methanol as modifier might be difficult, as this is a widely used modifier providing good solubility when analyzing polar compounds in SFC. A sample preparation with e.g. LLE would remove the alkali ions, however also introducing a time consuming and discriminating step into the method. Since the alkali metal ions were retained and affected by chromatographic adjustments as e.g. mobile phase modifications, a way to avoid them could therefore be chromatographic tuning, when analyzing samples containing them. Copyright © 2018 Elsevier B.V. All rights reserved.

Effect of Alkali Metal Cations on Slow Inactivation of Cardiac Na+ Channels

PubMed Central

Townsend, Claire; Horn, Richard

1997-01-01

Human heart Na+ channels were expressed transiently in both mammalian cells and Xenopus oocytes, and Na+ currents measured using 150 mM intracellular Na+. The kinetics of decaying outward Na+ current in response to 1-s depolarizations in the F1485Q mutant depends on the predominant cation in the extracellular solution, suggesting an effect on slow inactivation. The decay rate is lower for the alkali metal cations Li+, Na+, K+, Rb+, and Cs+ than for the organic cations Tris, tetramethylammonium, N-methylglucamine, and choline. In whole cell recordings, raising [Na+]o from 10 to 150 mM increases the rate of recovery from slow inactivation at −140 mV, decreases the rate of slow inactivation at relatively depolarized voltages, and shifts steady-state slow inactivation in a depolarized direction. Single channel recordings of F1485Q show a decrease in the number of blank (i.e., null) records when [Na+]o is increased. Significant clustering of blank records when depolarizing at a frequency of 0.5 Hz suggests that periods of inactivity represent the sojourn of a channel in a slow-inactivated state. Examination of the single channel kinetics at +60 mV during 90-ms depolarizations shows that neither open time, closed time, nor first latency is significantly affected by [Na+]o. However raising [Na+]o decreases the duration of the last closed interval terminated by the end of the depolarization, leading to an increased number of openings at the depolarized voltage. Analysis of single channel data indicates that at a depolarized voltage a single rate constant for entry into a slow-inactivated state is reduced in high [Na+]o, suggesting that the binding of an alkali metal cation, perhaps in the ion-conducting pore, inhibits the closing of the slow inactivation gate. PMID:9234168

Brimstone chemistry under laser light assists mass spectrometric detection and imaging the distribution of arsenic in minerals.

PubMed

Lal, Swapnil; Zheng, Zhaoyu; Pavlov, Julius; Attygalle, Athula B

2018-05-23

Singly charged As2n+1 ion clusters (n = 2-11) were generated from elemental arsenic by negative-ion laser-ablation mass spectrometry. The overall abundance of the gaseous As ions generated upon laser irradiation was enhanced nearly a hundred times when As-bearing samples were admixed with sulfur. However, sulfur does not act purely as an inert matrix: irradiating arsenic-sulfur mixtures revealed a novel pathway to generate and detect a series of [AsSn]- clusters (n = 2-6). Intriguingly, the spectra recorded from As2O3, NaAsO2, Na3AsO4, cacodylic acid and 3-amino-4-hydroxyphenylarsonic acid together with sulfur as the matrix were remarkably similar to that acquired from an elemental arsenic and sulfur mixture. This result indicated that arsenic sulfide cluster-ions are generated directly from arsenic compounds by a hitherto unknown pathway. The mechanism of elemental sulfur extracting chemically bound arsenic from compounds and forming [AsSn]- clusters is enigmatic; however, this discovery has a practical value as a general detection method for arsenic compounds. For example, the method was employed for the detection of As in its minerals, and for the imaging of arsenic distribution in minerals such as domeykite. LDI-MS data recorded from a latent image imprinted on a piece of paper from a flat mineral surface, and wetting the paper with a solution of sulfur, enabled the localization of arsenic in the mineral. The distribution of As was visualized as false-color images by extracting from acquired data the relative intensities of m/z 139 (AsS2-) and m/z 171 (AsS3-) ions.

Theoretical investigations on the d-p hybridized aromaticity, photoelectron spectroscopy and neutral salts of the LaX2- (X=Al, Ga, In) clusters.

PubMed

Chen, Jing; Yang, Huan; Wang, Jing; Cheng, Shi-Bo

2018-05-30

We present an extensive density functional theory (DFT) calculations on the geometrical and electronic structures of the triatomic LaX 2 - (X=Al, Ga, In) clusters. Various trail structures and spin states have been attempted to determine the lowest-energy geometries of these La-doped metal clusters. The ground states of all three clusters are calculated to possess the trigonal structures with the singlet multiplicities. The calculations on molecular orbitals (MOs) and nucleus-independent chemical shift (NICS) values have been performed to examine the aromatic characteristics of the LaX 2 - (X=Al, Ga, In) clusters. The present calculations disclose that all these metal clusters are doubly aromatic, namely d-p hybridized σ and π aromaticity resulting from the effective overlap between the 5d atomic orbital of the La atom and the p orbitals of the IIIA group elements. Theoretical vertical detachment energies (VDEs) were also calculated to simulate the photoelectron spectra (PES) of the clusters. In addition, by adding the alkali cations (Li + and Na + ) into the LaX 2 - (X=Al, Ga, In) clusters, the geometries and electronic structures of the corresponding neutral salts have also been investigated to gain more insights in the potential of using these aromatic anions as building blocks. Copyright © 2018 Elsevier B.V. All rights reserved.

Molecular-dynamics analysis of mobile helium cluster reactions near surfaces of plasma-exposed tungsten

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

Hu, Lin; Maroudas, Dimitrios, E-mail: maroudas@ecs.umass.edu; Hammond, Karl D.

We report the results of a systematic atomic-scale analysis of the reactions of small mobile helium clusters (He{sub n}, 4 ≤ n ≤ 7) near low-Miller-index tungsten (W) surfaces, aiming at a fundamental understanding of the near-surface dynamics of helium-carrying species in plasma-exposed tungsten. These small mobile helium clusters are attracted to the surface and migrate to the surface by Fickian diffusion and drift due to the thermodynamic driving force for surface segregation. As the clusters migrate toward the surface, trap mutation (TM) and cluster dissociation reactions are activated at rates higher than in the bulk. TM produces W adatoms and immobile complexes ofmore » helium clusters surrounding W vacancies located within the lattice planes at a short distance from the surface. These reactions are identified and characterized in detail based on the analysis of a large number of molecular-dynamics trajectories for each such mobile cluster near W(100), W(110), and W(111) surfaces. TM is found to be the dominant cluster reaction for all cluster and surface combinations, except for the He{sub 4} and He{sub 5} clusters near W(100) where cluster partial dissociation following TM dominates. We find that there exists a critical cluster size, n = 4 near W(100) and W(111) and n = 5 near W(110), beyond which the formation of multiple W adatoms and vacancies in the TM reactions is observed. The identified cluster reactions are responsible for important structural, morphological, and compositional features in the plasma-exposed tungsten, including surface adatom populations, near-surface immobile helium-vacancy complexes, and retained helium content, which are expected to influence the amount of hydrogen re-cycling and tritium retention in fusion tokamaks.« less

Choosing appropriate analysis methods for cluster randomised cross-over trials with a binary outcome.

PubMed

Morgan, Katy E; Forbes, Andrew B; Keogh, Ruth H; Jairath, Vipul; Kahan, Brennan C

2017-01-30

In cluster randomised cross-over (CRXO) trials, clusters receive multiple treatments in a randomised sequence over time. In such trials, there is usual correlation between patients in the same cluster. In addition, within a cluster, patients in the same period may be more similar to each other than to patients in other periods. We demonstrate that it is necessary to account for these correlations in the analysis to obtain correct Type I error rates. We then use simulation to compare different methods of analysing a binary outcome from a two-period CRXO design. Our simulations demonstrated that hierarchical models without random effects for period-within-cluster, which do not account for any extra within-period correlation, performed poorly with greatly inflated Type I errors in many scenarios. In scenarios where extra within-period correlation was present, a hierarchical model with random effects for cluster and period-within-cluster only had correct Type I errors when there were large numbers of clusters; with small numbers of clusters, the error rate was inflated. We also found that generalised estimating equations did not give correct error rates in any scenarios considered. An unweighted cluster-level summary regression performed best overall, maintaining an error rate close to 5% for all scenarios, although it lost power when extra within-period correlation was present, especially for small numbers of clusters. Results from our simulation study show that it is important to model both levels of clustering in CRXO trials, and that any extra within-period correlation should be accounted for. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

An Approach to Cluster EU Member States into Groups According to Pathways of Salmonella in the Farm-to-Consumption Chain for Pork Products.

PubMed

Vigre, Håkan; Domingues, Ana Rita Coutinho Calado; Pedersen, Ulrik Bo; Hald, Tine

2016-03-01

The aim of the project as the cluster analysis was to in part to develop a generic structured quantitative microbiological risk assessment (QMRA) model of human salmonellosis due to pork consumption in EU member states (MSs), and the objective of the cluster analysis was to group the EU MSs according to the relative contribution of different pathways of Salmonella in the farm-to-consumption chain of pork products. In the development of the model, by selecting a case study MS from each cluster the model was developed to represent different aspects of pig production, pork production, and consumption of pork products across EU states. The objective of the cluster analysis was to aggregate MSs into groups of countries with similar importance of different pathways of Salmonella in the farm-to-consumption chain using available, and where possible, universal register data related to the pork production and consumption in each country. Based on MS-specific information about distribution of (i) small and large farms, (ii) small and large slaughterhouses, (iii) amount of pork meat consumed, and (iv) amount of sausages consumed we used nonhierarchical and hierarchical cluster analysis to group the MSs. The cluster solutions were validated internally using statistic measures and externally by comparing the clustered MSs with an estimated human incidence of salmonellosis due to pork products in the MSs. Finally, each cluster was characterized qualitatively using the centroids of the clusters. © 2016 Society for Risk Analysis.

Does Core Area Theory Apply to STIs in Rural Environments?

PubMed Central

Gesink, Dionne C; Sullivan, Ashleigh B; Norwood, Todd; Serre, Marc L; Miller, William C

2012-01-01

Background Our objective was to determine the extent to which geographical core areas for gonorrhea and syphilis are located in rural areas, as compared to urban areas. Methods Incident gonorrhea (January 1, 2005 to December 31, 2010) and syphilis (January 1, 1999 to December 31, 2010) rates were estimated and mapped by census tract and quarter. Rurality was measured using percent rural and rural-urban commuting area (RUCA; rural, small town, micropolitan, or urban). SaTScan was used to identify spatiotemporal clusters of significantly elevated rates of infection. Clusters lasting five years or longer were considered core areas; clusters of shorter duration were considered outbreaks. Clusters were overlaid on maps of rurality and qualitatively assessed for correlation. Results Twenty gonorrhea core areas were identified; 65% in urban centers, 25% in micropolitan areas, and the remaining 10% were geographically large capturing combinations of urban, micropolitan, small town and rural environments. Ten syphilis core areas were identified with 80% in urban centers and 20% capturing two or more RUCAs. All ten of the syphilis core areas (100%) overlapped with gonorrhea core areas. Conclusions Gonorrhea and syphilis rates were high for rural parts of North Carolina; however, no core areas were identified exclusively for small towns or rural areas. The main pathway of rural STI transmission may be through the interconnectedness of urban, micropolitan, small town and rural areas. Directly addressing STIs in urban and micropolitan communities may also indirectly help address STI rates in rural and small town communities. PMID:23254115

Clean Water State Revolving Fund (CWSRF): Decentralized Wastewater Treatment

EPA Pesticide Factsheets

Decentralized wastewater treatment is an onsite or clustered system used to collect, treat, and disperse or reclaim wastewater from a small community or service area (e.g., septic systems, cluster systems, lagoons).

FAST TRACK COMMUNICATION A DFT + DMFT approach for nanosystems

NASA Astrophysics Data System (ADS)

Turkowski, Volodymyr; Kabir, Alamgir; Nayyar, Neha; Rahman, Talat S.

2010-11-01

We propose a combined density-functional-theory-dynamical-mean-field-theory (DFT + DMFT) approach for reliable inclusion of electron-electron correlation effects in nanosystems. Compared with the widely used DFT + U approach, this method has several advantages, the most important of which is that it takes into account dynamical correlation effects. The formalism is illustrated through different calculations of the magnetic properties of a set of small iron clusters (number of atoms 2 <= N <= 5). It is shown that the inclusion of dynamical effects leads to a reduction in the cluster magnetization (as compared to results from DFT + U) and that, even for such small clusters, the magnetization values agree well with experimental estimations. These results justify confidence in the ability of the method to accurately describe the magnetic properties of clusters of interest to nanoscience.

A quasichemical approach for protein-cluster free energies in dilute solution

NASA Astrophysics Data System (ADS)

Young, Teresa M.; Roberts, Christopher J.

2007-10-01

Reversible formation of protein oligomers or small clusters is a key step in processes such as protein polymerization, fibril formation, and protein phase separation from dilute solution. A straightforward, statistical mechanical approach to accurately calculate cluster free energies in solution is presented using a cell-based, quasichemical (QC) approximation for the partition function of proteins in an implicit solvent. The inputs to the model are the protein potential of mean force (PMF) and the corresponding subcell degeneracies up to relatively low particle densities. The approach is tested using simple two and three dimensional lattice models in which proteins interact with either isotropic or anisotropic nearest-neighbor attractions. Comparison with direct Monte Carlo simulation shows that cluster probabilities and free energies of oligomer formation (ΔGi0) are quantitatively predicted by the QC approach for protein volume fractions ˜10-2 (weight/volume concentration ˜10gl-1) and below. For small clusters, ΔGi0 depends weakly on the strength of short-ranged attractive interactions for most experimentally relevant values of the normalized osmotic second virial coefficient (b2*). For larger clusters (i ≫2), there is a small but non-negligible b2* dependence. The results suggest that nonspecific, hydrophobic attractions may not significantly stabilize prenuclei in processes such as non-native aggregation. Biased Monte Carlo methods are shown to accurately provide subcell degeneracies that are intractable to obtain analytically or by direct enumeration, and so offer a means to generalize the approach to mixtures and proteins with more complex PMFs.

Angle-Resolved Photoemission of Solvated Electrons in Sodium-Doped Clusters.

PubMed

West, Adam H C; Yoder, Bruce L; Luckhaus, David; Saak, Clara-Magdalena; Doppelbauer, Maximilian; Signorell, Ruth

2015-04-16

Angle-resolved photoelectron spectroscopy of the unpaired electron in sodium-doped water, methanol, ammonia, and dimethyl ether clusters is presented. The experimental observations and the complementary calculations are consistent with surface electrons for the cluster size range studied. Evidence against internally solvated electrons is provided by the photoelectron angular distribution. The trends in the ionization energies seem to be mainly determined by the degree of hydrogen bonding in the solvent and the solvation of the ion core. The onset ionization energies of water and methanol clusters do not level off at small cluster sizes but decrease slightly with increasing cluster size.

Red giants and yellow stragglers in the young open cluster NGC 2447

NASA Astrophysics Data System (ADS)

da Silveira, M. D.; Pereira, C. B.; Drake, N. A.

2018-06-01

In this work we analysed, using high-resolution spectroscopy, a sample of 12 single and 4 spectroscopic binary stars of the open cluster NGC 2447. For the single stars, we obtained atmospheric parameters and chemical abundances of Li, C, N, O, Na, Mg, Al, Ca, Si, Ti, Ni, Cr, Y, Zr, La, Ce, Nd, Eu. Rotational velocities were obtained for all the stars. The abundances of the light elements and Eu and the rotational velocities were derived using spectral synthesis technique. We obtained a mean metallicity of [Fe/H] = -0.17 ± 0.05. We found that the abundances of all elements are similar to field giants and/or giants of open clusters, even for the s-process elements, which are enhanced as in other young open clusters. We show that the spectroscopic binaries NGC 2447-26, 38, and 42 are yellow-straggler stars, of which the primary is a giant star and the secondary a main-sequence A-type star.

Progress toward Synthesis and Characterization of Rare-Earth Nanoparticles

NASA Astrophysics Data System (ADS)

Romero, Dulce G.; Ho, Pei-Chun; Attar, Saeed; Margosan, Dennis

2010-03-01

Magnetic nanoparticles exhibit interesting phenomena, such as enhanced magnetization and reduced magnetic ordering temperature (i.e. superparamagnetism), which has technical applications in industry, including magnetic storage, magnetic imaging, and magnetic refrigeration. We used the inverse micelle technique to synthesize Gd and Nd nanoparticles given its potential to control the cluster size, amount of aggregation, and prevent oxidation of the rare-earth elements. Gd and Nd were reduced by NaBH4 from the chloride salt. The produced clusters were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The results from the XRD show that the majority of the peaks match those of the surfactant, DDAB. No peaks of Gd were observed due to excess surfactant or amorphous clusters. However, the results from the SEM and EDX indicate the presence of Gd and Nd in our clusters microscopically, and current synthesized samples contain impurities. We are using liquid-liquid extraction method to purify the sample, and the results will be discussed.

Clusters of Galaxies at High Redshift

NASA Astrophysics Data System (ADS)

Fort, Bernard

For a long time, the small number of clusters at z > 0.3 in the Abell survey catalogue and simulations of the standard CDM formation of large scale structures provided a paradigm where clusters were considered as young merging structures. At earlier times, loose concentrations of galaxy clumps were mostly anticipated. Recent observations broke the taboo. Progressively we became convinced that compact and massive clusters at z = 1 or possibly beyond exist and should be searched for.

M87 at 90 Centimeters: A Different Picture

DTIC Science & Technology

2000-06-15

as is envisioned in the cooling Ñow model. Subject headings : cooling Ñows È galaxies : active È galaxies : clusters : individual ( Virgo ) È galaxies...atmosphere of the Virgo Cluster (Fabricant, Lecar, & Gorenstein 1980). The X-ray atmosphere has a simple, apparently undis- turbed, morphology with a central...of a small set of amorphous central radio galaxies in other, similar, cooling-core clusters ? 4. PHYSICAL PICTURE : THE CLUSTER CORE The Virgo X-ray

ROSAT PSPC Observations of CL0016+16

NASA Technical Reports Server (NTRS)

Hughes, John P. (Principal Investigator)

1996-01-01

Several ROSAT observations concerning with complex spatial structures in Sunyaev-Zel'dovich decrement clusters Abell 665 and CL0016+16, discovery of Be/X-ray stars in two supernova remnants in the Small Magellanic Cloud, a new transient pulsar in the Small Magellanic Cloud with an unusual x-ray spectrum, a new x-ray-discovered cluster of galaxies associated with CL0016+16, and the distance to CL0016+16 vs. the Hubble constant, are presented.

Structures, electronic properties and reaction paths from Fe(CO)5 molecule to small Fe clusters

NASA Astrophysics Data System (ADS)

Li, Zhi; Zhao, Zhen

2018-04-01

The geometries, electrical characters and reaction paths from Fe(CO)5 molecule to small Fe clusters were investigated by using all-electron density functional theory. The results show that in the decomposition process of pentacarbonyl-iron, Fe(CO)5 molecule prefers to remove a carbon monoxide and adsorb another Fe(CO)5 molecule to produce nonacarbonyldiiron Fe2(CO)9 then Fe2(CO)9 gradually removes carbon monoxide to produce small Fe clusters. As It can be seen from the highest occupied molecule orbital-lowest unoccupied molecule orbital gap curves, the Fe(CO)n=3, and 5 and Fe2(CO)n=3, 7 and 9 intermediates have higher chemical stability than their neighbors. The local magnetic moment of the carbon monoxide is aligning anti-ferromagnetic. The effect of external magnetic field to the initial decomposition products of Fe(CO)5 can be ignored.

Inference With Difference-in-Differences With a Small Number of Groups: A Review, Simulation Study, and Empirical Application Using SHARE Data.

PubMed

Rokicki, Slawa; Cohen, Jessica; Fink, Günther; Salomon, Joshua A; Landrum, Mary Beth

2018-01-01

Difference-in-differences (DID) estimation has become increasingly popular as an approach to evaluate the effect of a group-level policy on individual-level outcomes. Several statistical methodologies have been proposed to correct for the within-group correlation of model errors resulting from the clustering of data. Little is known about how well these corrections perform with the often small number of groups observed in health research using longitudinal data. First, we review the most commonly used modeling solutions in DID estimation for panel data, including generalized estimating equations (GEE), permutation tests, clustered standard errors (CSE), wild cluster bootstrapping, and aggregation. Second, we compare the empirical coverage rates and power of these methods using a Monte Carlo simulation study in scenarios in which we vary the degree of error correlation, the group size balance, and the proportion of treated groups. Third, we provide an empirical example using the Survey of Health, Ageing, and Retirement in Europe. When the number of groups is small, CSE are systematically biased downwards in scenarios when data are unbalanced or when there is a low proportion of treated groups. This can result in over-rejection of the null even when data are composed of up to 50 groups. Aggregation, permutation tests, bias-adjusted GEE, and wild cluster bootstrap produce coverage rates close to the nominal rate for almost all scenarios, though GEE may suffer from low power. In DID estimation with a small number of groups, analysis using aggregation, permutation tests, wild cluster bootstrap, or bias-adjusted GEE is recommended.

Follow up of stellar migrants from globular clusters using the Hobby-Eberly Telescope

NASA Astrophysics Data System (ADS)

Shetrone, Matthew D.; Martell, Sarah L.

2017-01-01

Nearly all globular clusters contain at least two populations of stars. The first generation has abundances very similar to that of the average Milky Way halo stars at that metallicity. The second generation, presumably polluted by the massive stars of the first generation, have abundance patterns which include lower abundances of C, O, and Mg and higher abundances of N, Al and Na compared to first generation. Martell & Grebel (2010) identified a number of potential second generation stars using the CH and CN bandstrengths from SDSS-II/SEGUE spectra. We have followed up these candidates with moderate resolution spectra using HRS on the Hobby-Eberly Telescope. We present the success rate of finding globular cluster migrants and discuss the reasons why some stars exhibit a CN false positive signal in CN and CH.

Theoretical research program to study transition metal trimers and embedded clusters

NASA Technical Reports Server (NTRS)

Walch, Stephen P.

1987-01-01

The results of ab-initio calculations are reported for (1) small transition metal clusters and (2) potential energy surfaces for chemical reactions important in hydrogen combustion and high temperature air chemistry.

Integrated Control of Na Transport along the Nephron

PubMed Central

Schnermann, Jürgen

2015-01-01

The kidney filters vast quantities of Na at the glomerulus but excretes a very small fraction of this Na in the final urine. Although almost every nephron segment participates in the reabsorption of Na in the normal kidney, the proximal segments (from the glomerulus to the macula densa) and the distal segments (past the macula densa) play different roles. The proximal tubule and the thick ascending limb of the loop of Henle interact with the filtration apparatus to deliver Na to the distal nephron at a rather constant rate. This involves regulation of both filtration and reabsorption through the processes of glomerulotubular balance and tubuloglomerular feedback. The more distal segments, including the distal convoluted tubule (DCT), connecting tubule, and collecting duct, regulate Na reabsorption to match the excretion with dietary intake. The relative amounts of Na reabsorbed in the DCT, which mainly reabsorbs NaCl, and by more downstream segments that exchange Na for K are variable, allowing the simultaneous regulation of both Na and K excretion. PMID:25098598

Mini-clusters

NASA Technical Reports Server (NTRS)

Chinellato, J. A.; Dobrigkeit, C.; Bellandifilho, J.; Lattes, C. M. G.; Menon, M. J.; Navia, C. E.; Pamilaju, A.; Sawayanagi, K.; Shibuya, E. H.; Turtelli, A., Jr.

1985-01-01

Experimental results of mini-clusters observed in Chacaltaya emulsion chamber no.19 are summarized. The study was made on 54 single core shower upper and 91 shower clusters of E(gamma) 10 TeV from 30 families which are visible energy greater than 80 TeV and penetrate through both upper and lower detectors of the two-story chamber. The association of hadrons in mini-cluster is made clear from their penetrative nature and microscopic observation of shower continuation in lower chamber. Small P sub t (gamma) of hadrons in mini-clusters remained in puzzle.

Star Clusters in the Magellanic Clouds

NASA Astrophysics Data System (ADS)

Gallagher, J. S., III

2014-09-01

The Magellanic Clouds (MC) are prime locations for studies of star clusters covering a full range in age and mass. This contribution briefly reviews selected properties of Magellanic star clusters, by focusing first on young systems that show evidence for hierarchical star formation. The structures and chemical abundance patterns of older intermediate age star clusters in the Small Magellanic Cloud (SMC) are a second topic. These suggest a complex history has affected the chemical enrichment in the SMC and that low tidal stresses in the SMC foster star cluster survival.

Towards accurate modelling of galaxy clustering on small scales: testing the standard ΛCDM + halo model

NASA Astrophysics Data System (ADS)

Sinha, Manodeep; Berlind, Andreas A.; McBride, Cameron K.; Scoccimarro, Roman; Piscionere, Jennifer A.; Wibking, Benjamin D.

2018-07-01

Interpreting the small-scale clustering of galaxies with halo models can elucidate the connection between galaxies and dark matter haloes. Unfortunately, the modelling is typically not sufficiently accurate for ruling out models statistically. It is thus difficult to use the information encoded in small scales to test cosmological models or probe subtle features of the galaxy-halo connection. In this paper, we attempt to push halo modelling into the `accurate' regime with a fully numerical mock-based methodology and careful treatment of statistical and systematic errors. With our forward-modelling approach, we can incorporate clustering statistics beyond the traditional two-point statistics. We use this modelling methodology to test the standard Λ cold dark matter (ΛCDM) + halo model against the clustering of Sloan Digital Sky Survey (SDSS) seventh data release (DR7) galaxies. Specifically, we use the projected correlation function, group multiplicity function, and galaxy number density as constraints. We find that while the model fits each statistic separately, it struggles to fit them simultaneously. Adding group statistics leads to a more stringent test of the model and significantly tighter constraints on model parameters. We explore the impact of varying the adopted halo definition and cosmological model and find that changing the cosmology makes a significant difference. The most successful model we tried (Planck cosmology with Mvir haloes) matches the clustering of low-luminosity galaxies, but exhibits a 2.3σ tension with the clustering of luminous galaxies, thus providing evidence that the `standard' halo model needs to be extended. This work opens the door to adding interesting freedom to the halo model and including additional clustering statistics as constraints.

Clustering on very small scales from a large sample of confirmed quasar pairs: does quasar clustering track from Mpc to kpc scales?

NASA Astrophysics Data System (ADS)

Eftekharzadeh, S.; Myers, A. D.; Hennawi, J. F.; Djorgovski, S. G.; Richards, G. T.; Mahabal, A. A.; Graham, M. J.

2017-06-01

We present the most precise estimate to date of the clustering of quasars on very small scales, based on a sample of 47 binary quasars with magnitudes of g < 20.85 and proper transverse separations of ˜25 h-1 kpc. Our sample of binary quasars, which is about six times larger than any previous spectroscopically confirmed sample on these scales, is targeted using a kernel density estimation (KDE) technique applied to Sloan Digital Sky Survey (SDSS) imaging over most of the SDSS area. Our sample is 'complete' in that all of the KDE target pairs with 17.0 ≲ R ≲ 36.2 h-1 kpc in our area of interest have been spectroscopically confirmed from a combination of previous surveys and our own long-slit observational campaign. We catalogue 230 candidate quasar pairs with angular separations of <8 arcsec, from which our binary quasars were identified. We determine the projected correlation function of quasars (\\bar{W}_p) in four bins of proper transverse scale over the range 17.0 ≲ R ≲ 36.2 h-1 kpc. The implied small-scale quasar clustering amplitude from the projected correlation function, integrated across our entire redshift range, is A = 24.1 ± 3.6 at ˜26.6 h-1 kpc. Our sample is the first spectroscopically confirmed sample of quasar pairs that is sufficiently large to study how quasar clustering evolves with redshift at ˜25 h-1 kpc. We find that empirical descriptions of how quasar clustering evolves with redshift at ˜25 h-1 Mpc also adequately describe the evolution of quasar clustering at ˜25 h-1 kpc.

CO-Bridged H-Cluster Intermediates in the Catalytic Mechanism of [FeFe]-Hydrogenase CaI

DOE PAGES

Ratzloff, Michael W.; Artz, Jacob H.; Mulder, David W.; ...

2018-05-23

The [FeFe]-hydrogenases ([FeFe] H 2ases) catalyze reversible H 2 activation at the H-cluster, which is composed of a [4Fe-4S] H subsite linked by a cysteine thiolate to a bridged, organometallic [2Fe-2S] ([2Fe] H) subsite. Profoundly different geometric models of the H-cluster redox states that orchestrate the electron/proton transfer steps of H 2 bond activation have been proposed. We have examined this question in the [FeFe] H 2ase I from Clostridium acetobutylicum (CaI) by Fourier-transform infrared (FTIR) spectroscopy with temperature annealing and H/D isotope exchange to identify the relevant redox states and define catalytic transitions. One-electron reduction of H ox ledmore » to formation of H redH + ([4Fe-4S] H 2+-Fe I-Fe I) and H red' ([4Fe-4S] H 1+-Fe II-Fe I), with both states characterized by low frequency μ-CO IR modes consistent with a fully bridged [2Fe] H. Similar μ-CO IR modes were also identified for H redH + of the [FeFe] H 2ase from Chlamydomonas reinhardtii (CrHydA1). The CaI proton-transfer variant C298S showed enrichment of an H/D isotope-sensitive μ-CO mode, a component of the hydride bound H-cluster IR signal, H hyd. Equilibrating CaI with increasing amounts of NaDT, and probed at cryogenic temperatures, showed H redH + was converted to H hyd. Over an increasing temperature range from 10 to 260 K catalytic turnover led to loss of Hhyd and appearance of H ox, consistent with enzymatic turnover and H 2 formation. The results show for CaI that the μ-CO of [2Fe] H remains bridging for all of the 'H red' states and that H redH + is on pathway to H hyd and H 2 evolution in the catalytic mechanism. Here, this provides a blueprint for designing small molecule catalytic analogs« less

CO-Bridged H-Cluster Intermediates in the Catalytic Mechanism of [FeFe]-Hydrogenase CaI

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

Ratzloff, Michael W.; Artz, Jacob H.; Mulder, David W.

The [FeFe]-hydrogenases ([FeFe] H 2ases) catalyze reversible H 2 activation at the H-cluster, which is composed of a [4Fe-4S] H subsite linked by a cysteine thiolate to a bridged, organometallic [2Fe-2S] ([2Fe] H) subsite. Profoundly different geometric models of the H-cluster redox states that orchestrate the electron/proton transfer steps of H 2 bond activation have been proposed. We have examined this question in the [FeFe] H 2ase I from Clostridium acetobutylicum (CaI) by Fourier-transform infrared (FTIR) spectroscopy with temperature annealing and H/D isotope exchange to identify the relevant redox states and define catalytic transitions. One-electron reduction of H ox ledmore » to formation of H redH + ([4Fe-4S] H 2+-Fe I-Fe I) and H red' ([4Fe-4S] H 1+-Fe II-Fe I), with both states characterized by low frequency μ-CO IR modes consistent with a fully bridged [2Fe] H. Similar μ-CO IR modes were also identified for H redH + of the [FeFe] H 2ase from Chlamydomonas reinhardtii (CrHydA1). The CaI proton-transfer variant C298S showed enrichment of an H/D isotope-sensitive μ-CO mode, a component of the hydride bound H-cluster IR signal, H hyd. Equilibrating CaI with increasing amounts of NaDT, and probed at cryogenic temperatures, showed H redH + was converted to H hyd. Over an increasing temperature range from 10 to 260 K catalytic turnover led to loss of Hhyd and appearance of H ox, consistent with enzymatic turnover and H 2 formation. The results show for CaI that the μ-CO of [2Fe] H remains bridging for all of the 'H red' states and that H redH + is on pathway to H hyd and H 2 evolution in the catalytic mechanism. Here, this provides a blueprint for designing small molecule catalytic analogs« less

CO-Bridged H-Cluster Intermediates in the Catalytic Mechanism of [FeFe]-Hydrogenase CaI.

PubMed

Ratzloff, Michael W; Artz, Jacob H; Mulder, David W; Collins, Reuben T; Furtak, Thomas E; King, Paul W

2018-06-20

The [FeFe]-hydrogenases ([FeFe] H 2 ases) catalyze reversible H 2 activation at the H-cluster, which is composed of a [4Fe-4S] H subsite linked by a cysteine thiolate to a bridged, organometallic [2Fe-2S] ([2Fe] H ) subsite. Profoundly different geometric models of the H-cluster redox states that orchestrate the electron/proton transfer steps of H 2 bond activation have been proposed. We have examined this question in the [FeFe] H 2 ase I from Clostridium acetobutylicum (CaI) by Fourier-transform infrared (FTIR) spectroscopy with temperature annealing and H/D isotope exchange to identify the relevant redox states and define catalytic transitions. One-electron reduction of H ox led to formation of H red H + ([4Fe-4S] H 2+ -Fe I -Fe I ) and H red ' ([4Fe-4S] H 1+ -Fe II -Fe I ), with both states characterized by low frequency μ-CO IR modes consistent with a fully bridged [2Fe] H . Similar μ-CO IR modes were also identified for H red H + of the [FeFe] H 2 ase from Chlamydomonas reinhardtii (CrHydA1). The CaI proton-transfer variant C298S showed enrichment of an H/D isotope-sensitive μ-CO mode, a component of the hydride bound H-cluster IR signal, H hyd . Equilibrating CaI with increasing amounts of NaDT, and probed at cryogenic temperatures, showed H red H + was converted to H hyd . Over an increasing temperature range from 10 to 260 K catalytic turnover led to loss of H hyd and appearance of H ox , consistent with enzymatic turnover and H 2 formation. The results show for CaI that the μ-CO of [2Fe] H remains bridging for all of the "H red " states and that H red H + is on pathway to H hyd and H 2 evolution in the catalytic mechanism. These results provide a blueprint for designing small molecule catalytic analogs.

Five ab initio potential energy and dipole moment surfaces for hydrated NaCl and NaF. I. Two-body interactions

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

Wang, Yimin, E-mail: yimin.wang@emory.edu; Bowman, Joel M., E-mail: jmbowma@emory.edu; Kamarchik, Eugene, E-mail: eugene.kamarchik@gmail.com

2016-03-21

We report full-dimensional, ab initio-based potentials and dipole moment surfaces for NaCl, NaF, Na{sup +}H{sub 2}O, F{sup −}H{sub 2}O, and Cl{sup −}H{sub 2}O. The NaCl and NaF potentials are diabatic ones that dissociate to ions. These are obtained using spline fits to CCSD(T)/aug-cc-pV5Z energies. In addition, non-linear least square fits using the Born-Mayer-Huggins potential are presented, providing accurate parameters based strictly on the current ab initio energies. The long-range behavior of the NaCl and NaF potentials is shown to go, as expected, accurately to the point-charge Coulomb interaction. The three ion-H{sub 2}O potentials are permutationally invariant fits to roughly 20 000more » coupled cluster CCSD(T) energies (awCVTZ basis for Na{sup +} and aVTZ basis for Cl{sup −} and F{sup −}), over a large range of distances and H{sub 2}O intramolecular configurations. These potentials are switched accurately in the long range to the analytical ion-dipole interactions, to improve computational efficiency. Dipole moment surfaces are fits to MP2 data; for the ion-ion cases, these are well described in the intermediate- and long-range by the simple point-charge expression. The performance of these new fits is examined by direct comparison to additional ab initio energies and dipole moments along various cuts. Equilibrium structures, harmonic frequencies, and electronic dissociation energies are also reported and compared to direct ab initio results. These indicate the high fidelity of the new PESs.« less

Solvation behavior of carbonate-based electrolytes in sodium ion batteries.

PubMed

Cresce, Arthur V; Russell, Selena M; Borodin, Oleg; Allen, Joshua A; Schroeder, Marshall A; Dai, Michael; Peng, Jing; Gobet, Mallory P; Greenbaum, Steven G; Rogers, Reginald E; Xu, Kang

2016-12-21

Sodium ion batteries are on the cusp of being a commercially available technology. Compared to lithium ion batteries, sodium ion batteries can potentially offer an attractive dollar-per-kilowatt-hour value, though at the penalty of reduced energy density. As a materials system, sodium ion batteries present a unique opportunity to apply lessons learned in the study of electrolytes for lithium ion batteries; specifically, the behavior of the sodium ion in an organic carbonate solution and the relationship of ion solvation with electrode surface passivation. In this work the Li + and Na + -based solvates were characterized using electrospray mass spectrometry, infrared and Raman spectroscopy, 17 O, 23 Na and pulse field gradient double-stimulated-echo pulse sequence nuclear magnetic resonance (NMR), and conductivity measurements. Spectroscopic evidence demonstrate that the Li + and Na + cations share a number of similar ion-solvent interaction trends, such as a preference in the gas and liquid phase for a solvation shell rich in cyclic carbonates over linear carbonates and fluorinated carbonates. However, quite different IR spectra due to the PF 6 - anion interactions with the Na + and Li + cations were observed and were rationalized with the help of density functional theory (DFT) calculations that were also used to examine the relative free energies of solvates using cluster - continuum models. Ion-solvent distances for Na + were longer than Li + , and Na + had a greater tendency towards forming contact pairs compared to Li + in linear carbonate solvents. In tests of hard carbon Na-ion batteries, performance was not well correlated to Na + solvent preference, leading to the possibility that Na + solvent preference may play a reduced role in the passivation of anode surfaces and overall Na-ion battery performance.

Inferring HIV-1 Transmission Dynamics in Germany From Recently Transmitted Viruses.

PubMed

Pouran Yousef, Kaveh; Meixenberger, Karolin; Smith, Maureen R; Somogyi, Sybille; Gromöller, Silvana; Schmidt, Daniel; Gunsenheimer-Bartmeyer, Barbara; Hamouda, Osamah; Kücherer, Claudia; von Kleist, Max

2016-11-01

Although HIV continues to spread globally, novel intervention strategies such as treatment as prevention (TasP) may bring the epidemic to a halt. However, their effective implementation requires a profound understanding of the underlying transmission dynamics. We analyzed parameters of the German HIV epidemic based on phylogenetic clustering of viral sequences from recently infected seroconverters with known infection dates. Viral baseline and follow-up pol sequences (n = 1943) from 1159 drug-naïve individuals were selected from a nationwide long-term observational study initiated in 1997. Putative transmission clusters were computed based on a maximum likelihood phylogeny. Using individual follow-up sequences, we optimized our clustering threshold to maximize the likelihood of co-clustering individuals connected by direct transmission. The sizes of putative transmission clusters scaled inversely with their abundance and their distribution exhibited a heavy tail. Clusters based on the optimal clustering threshold were significantly more likely to contain members of the same or bordering German federal states. Interinfection times between co-clustered individuals were significantly shorter (26 weeks; interquartile range: 13-83) than in a null model. Viral intraindividual evolution may be used to select criteria that maximize co-clustering of transmission pairs in the absence of strong adaptive selection pressure. Interinfection times of co-clustered individuals may then be an indicator of the typical time to onward transmission. Our analysis suggests that onward transmission may have occurred early after infection, when individuals are typically unaware of their serological status. The latter argues that TasP should be combined with HIV testing campaigns to reduce the possibility of transmission before TasP initiation.

Optimizing modelling in iterative image reconstruction for preclinical pinhole PET

NASA Astrophysics Data System (ADS)

Goorden, Marlies C.; van Roosmalen, Jarno; van der Have, Frans; Beekman, Freek J.

2016-05-01

The recently developed versatile emission computed tomography (VECTor) technology enables high-energy SPECT and simultaneous SPECT and PET of small animals at sub-mm resolutions. VECTor uses dedicated clustered pinhole collimators mounted in a scanner with three stationary large-area NaI(Tl) gamma detectors. Here, we develop and validate dedicated image reconstruction methods that compensate for image degradation by incorporating accurate models for the transport of high-energy annihilation gamma photons. Ray tracing software was used to calculate photon transport through the collimator structures and into the gamma detector. Input to this code are several geometric parameters estimated from system calibration with a scanning 99mTc point source. Effects on reconstructed images of (i) modelling variable depth-of-interaction (DOI) in the detector, (ii) incorporating photon paths that go through multiple pinholes (‘multiple-pinhole paths’ (MPP)), and (iii) including various amounts of point spread function (PSF) tail were evaluated. Imaging 18F in resolution and uniformity phantoms showed that including large parts of PSFs is essential to obtain good contrast-noise characteristics and that DOI modelling is highly effective in removing deformations of small structures, together leading to 0.75 mm resolution PET images of a hot-rod Derenzo phantom. Moreover, MPP modelling reduced the level of background noise. These improvements were also clearly visible in mouse images. Performance of VECTor can thus be significantly improved by accurately modelling annihilation gamma photon transport.

Formation of supramolecular clusters at the interface of zeolite X following the adsorption of rare-earth cations and their impact on the macroscopic properties of the zeolite.

PubMed

Guzzinati, Roberta; Sarti, Elena; Catani, Martina; Costa, Valentina; Pagnoni, Antonella; Martucci, Annalisa; Rodeghero, Elisa; Capitani, Donatella; Pietrantonio, Massimiliana; Cavazzini, Alberto; Pasti, Luisa

2018-05-18

The adsorption behavior of neodymium (Nd3+) and yttrium (Y3+) cations on synthetic FAU zeolite 13X in its sodium form (Na13X) has been investigated by means of an approach based on both macroscopic (namely, adsorption isotherm determination and thermal analysis) and microscopic measurements (including solid-state NMR spectroscopy and X-ray powder diffraction). The multidisciplinary study has revealed some unexpected features. Firstly, adsorption constants of cations are not correlated to their ionic radii (or hydration enthalpy). The adsorption constant of Y3+ on Na13X was indeed about twice that of Nd3+, which is the opposite of what could be expected based on the size of the cations. In addition, adsorption was accompanied by partial dealumination of the zeolite framework. The extent of dealumination changed depending on exchanged cations. It was more significant on the Nd-exchanged zeolite than on the Y-exchanged one. The most interesting finding of this study, however, is the presence of supramolecular clusters composed of water, Nd3+, residual sodium ions and extraframework aluminum at the interface of Nd-exchanged zeolite. The hypothesis that these host-guest complexes are responsible of the significantly different behavior exhibited by Na13X towards the adsorption/desorption of Nd3+ and Y3+ has been formulated. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Low-rank network decomposition reveals structural characteristics of small-world networks

NASA Astrophysics Data System (ADS)

Barranca, Victor J.; Zhou, Douglas; Cai, David

2015-12-01

Small-world networks occur naturally throughout biological, technological, and social systems. With their prevalence, it is particularly important to prudently identify small-world networks and further characterize their unique connection structure with respect to network function. In this work we develop a formalism for classifying networks and identifying small-world structure using a decomposition of network connectivity matrices into low-rank and sparse components, corresponding to connections within clusters of highly connected nodes and sparse interconnections between clusters, respectively. We show that the network decomposition is independent of node indexing and define associated bounded measures of connectivity structure, which provide insight into the clustering and regularity of network connections. While many existing network characterizations rely on constructing benchmark networks for comparison or fail to describe the structural properties of relatively densely connected networks, our classification relies only on the intrinsic network structure and is quite robust with respect to changes in connection density, producing stable results across network realizations. Using this framework, we analyze several real-world networks and reveal new structural properties, which are often indiscernible by previously established characterizations of network connectivity.

Emergent patterns in interacting neuronal sub-populations

NASA Astrophysics Data System (ADS)

Kamal, Neeraj Kumar; Sinha, Sudeshna

2015-05-01

We investigate an ensemble of coupled model neurons, consisting of groups of varying sizes and intrinsic dynamics, ranging from periodic to chaotic, where the inter-group coupling interaction is effectively like a dynamic signal from a different sub-population. We observe that the minority group can significantly influence the majority group. For instance, when a small chaotic group is coupled to a large periodic group, the chaotic group de-synchronizes. However, counter-intuitively, when a small periodic group couples strongly to a large chaotic group, it leads to complete synchronization in the majority chaotic population, which also spikes at the frequency of the small periodic group. It then appears that the small group of periodic neurons can act like a pacemaker for the whole network. Further, we report the existence of varied clustering patterns, ranging from sets of synchronized clusters to anti-phase clusters, governed by the interplay of the relative sizes and dynamics of the sub-populations. So these results have relevance in understanding how a group can influence the synchrony of another group of dynamically different elements, reminiscent of event-related synchronization/de-synchronization in complex networks.

Nanoscale Decoration of Electrode Surfaces with an STM

DTIC Science & Technology

1999-05-30

covered gold electrode surfaces at predetermined positions. First, metal is deposited electrochemically onto the STM tip, then the clusters are formed by a...onto the tip, the jump-to-contact occurs in the opposite direction leaving holes in the gold surface. The stability of the metal clusters against anodic...deposition, clusters, a surprisingly high stability of the small Ag Hg/HgSO4 for Ag deposition and a Pt wire for Ni clusters on gold against anodic

Paradoxes of the influence of small Ni impurity additions in a NaCl crystal on the kinetics of its magnetoplasticity

NASA Astrophysics Data System (ADS)

Alshits, V. I.; Darinskaya, E. V.; Koldaeva, M. V.; Petrzhik, E. A.

2016-01-01

A comparative study of magnetoplasticity in two types of NaCl crystals differing in impurity content only by a small Ni addition (0.06 ppm) in one of them, NaCl(Ni), has been carried out. Two methods of sample magnetic exposure were used: in a constant field B = 0-0.6 T and in crossed fields in the EPR scheme—the Earth's field B Earth (50 μT) and a variable pumping field tilde B( ˜ 1 μ T) at frequencies ν 1 MHz. In the experiments in the EPR scheme, the change of the field orientation from tilde B bot B_{Earth} to . {tilde B} |B_{Earth} led to almost complete suppression of the effect in the NaCl(Ni) crystals and reduced only slightly (approximately by 20%) the height of the resonance peak of dislocation mean paths in the crystals without Ni, with the amplitude of the mean paths in NaCl(Ni) in the orientation tilde B bot B_{Earth} having been appreciably lower than that in NaCl. In contrast, upon exposure to a constant magnetic field, a more intense effect was observed in the crystal with Ni. The threshold pumping field amplitude tilde B, below which the effect is absent under resonance conditions, for the NaCl(Ni) crystals turned out to be a factor of 5 smaller than that for NaCl, while the thresholds of a constant magnetic field coincide for both types of crystals. All these differences are discussed in detail and interpreted.

Formation of globular cluster candidates in merging proto-galaxies at high redshift: a view from the FIRE cosmological simulations

DOE PAGES

Kim, Ji-hoon; Ma, Xiangcheng; Grudić, Michael Y.; ...

2017-11-23

Using a state-of-the-art cosmological simulation of merging proto-galaxies at high redshift from the FIRE project, with explicit treatments of star formation and stellar feedback in the interstellar medium, we investigate the formation of star clusters and examine one of the formation hypotheses of present-day metal-poor globular clusters. Here, we find that frequent mergers in high-redshift proto-galaxies could provide a fertile environment to produce long-lasting bound star clusters. The violent merger event disturbs the gravitational potential and pushes a large gas mass of ≳ 10 5–6 M ⊙ collectively to high density, at which point it rapidly turns into stars beforemore » stellar feedback can stop star formation. The high dynamic range of the reported simulation is critical in realizing such dense star-forming clouds with a small dynamical time-scale, tff ≲ 3 Myr, shorter than most stellar feedback time-scales. Our simulation then allows us to trace how clusters could become virialized and tightly bound to survive for up to ~420 Myr till the end of the simulation. Finally, because the cluster's tightly bound core was formed in one short burst, and the nearby older stars originally grouped with the cluster tend to be preferentially removed, at the end of the simulation the cluster has a small age spread.« less

Formation of globular cluster candidates in merging proto-galaxies at high redshift: a view from the FIRE cosmological simulations

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

Kim, Ji-hoon; Ma, Xiangcheng; Grudić, Michael Y.

Using a state-of-the-art cosmological simulation of merging proto-galaxies at high redshift from the FIRE project, with explicit treatments of star formation and stellar feedback in the interstellar medium, we investigate the formation of star clusters and examine one of the formation hypotheses of present-day metal-poor globular clusters. Here, we find that frequent mergers in high-redshift proto-galaxies could provide a fertile environment to produce long-lasting bound star clusters. The violent merger event disturbs the gravitational potential and pushes a large gas mass of ≳ 10 5–6 M ⊙ collectively to high density, at which point it rapidly turns into stars beforemore » stellar feedback can stop star formation. The high dynamic range of the reported simulation is critical in realizing such dense star-forming clouds with a small dynamical time-scale, tff ≲ 3 Myr, shorter than most stellar feedback time-scales. Our simulation then allows us to trace how clusters could become virialized and tightly bound to survive for up to ~420 Myr till the end of the simulation. Finally, because the cluster's tightly bound core was formed in one short burst, and the nearby older stars originally grouped with the cluster tend to be preferentially removed, at the end of the simulation the cluster has a small age spread.« less

Effect of Spin Multiplicity in O2 Adsorption and Dissociation on Small Bimetallic AuAg Clusters.

PubMed

García-Cruz, Raúl; Poulain, Enrique; Hernández-Pérez, Isaías; Reyes-Nava, Juan A; González-Torres, Julio C; Rubio-Ponce, A; Olvera-Neria, Oscar

2017-08-17

To dispose of atomic oxygen, it is necessary the O 2 activation; however, an energy barrier must be overcome to break the O-O bond. This work presents theoretical calculations of the O 2 adsorption and dissociation on small pure Au n and Ag m and bimetallic Au n Ag m (n + m ≤ 6) clusters using the density functional theory (DFT) and the zeroth-order regular approximation (ZORA) to explicitly include scalar relativistic effects. The most stable Au n Ag m clusters contain a higher concentration of Au with Ag atoms located in the center of the cluster. The O 2 adsorption energy on pure and bimetallic clusters and the ensuing geometries depend on the spin multiplicity of the system. For a doublet multiplicity, O 2 is adsorbed in a bridge configuration, whereas for a triplet only one O-metal bond is formed. The charge transfer from metal toward O 2 occupies the σ* O-O antibonding natural bond orbital, which weakens the oxygen bond. The Au 3 ( 2 A) cluster presents the lowest activation energy to dissociate O 2 , whereas the opposite applies to the AuAg ( 3 A) system. In the O 2 activation, bimetallic clusters are not as active as pure Au n clusters due to the charge donated by Ag atoms being shared between O 2 and Au atoms.