bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical study of precession of circulating particles in tokamaks
Authors: BURDO O. S. , KOLESNICHENKO YA. I. , SIPILÄ S. , YAKOVENKO YU. V.
Published: January 2011

The toroidal precession of circulating particles in tokamaks is studied numerically. The dependence of the precession frequency on the magnetic shear, the elongation of the plasma cross-section, and plasma pressure is investigated. It is concluded that the analytical expressions for the precession frequency by Kolesnichenko et al. (2003 Phys. Plasmas10, 1449–1457) represent a reasonable approximation for the limit cases of tokamaks with circular cross-section and shearless tokamaks with elliptical cross-section. The precession frequency was calculated for non-circular tokamaks with magnetic shear. Based on the numerical results, an interpolation formula for the precession frequency is proposed.
Passion for the Antarctic: a short play
Authors: Moore Jason Kendall , León Wöppke Consuelo
Published: January 2011

Passion for the Antarctic is the third scene of Tangled destinies, a play written by Jason Kendall Moore, directed by María Angelica Luzzi, and performed by Daniela Meneses and the author. It opened on 17 July 2010, in Valparaíso, Chile, where it will run through the first week of September. The Center for Hemispheric and Polar Studies has funded its production to generate interest in U.S.–Chilean relations in the Antarctic and elsewhere.
Responses of fine roots to experimental nitrogen addition in a tropical lower montane rain forest, Panama
Authors: Adamek Markus , Corre Marife D. , Hölscher Dirk
Published: January 2011

Nitrogen (N) availability is a major control on fine-root growth and distribution with depth in forest soils. We investigated fine-root dynamics in response to N addition in a montane rain forest with N-limited above-ground production. Control and N-fertilized (125 kg urea-N ha−1y−1) treatments were laid out in a paired-plot design with four replicates (each 40 × 40 m). During 1.5 y of treatment, fine root-biomass, necromass and production were assessed by sequential coring at three soil depths (organic layer, 0–10 cm and 10–20 cm mineral soil), whereas fine-root redistribution with depth was assessed by ingrowth cores. Total fine-root biomass, necromass and production in the controls were 458 ± 21 g m−2, 101 ± 9 g m−2and 324 ± 33 g m−2y−1, respectively. No significant difference at any depth was detected under N fertilization. Fine-root biomass in the organic layer decreased over time under N addition. At 10–20 cm in the mineral soil, fine-root biomass in ingrowth cores increased significantly after 1.5 y of N fertilization compared with the control. The increased available N may have induced the change in fine-root distribution to explore the deeper mineral soil for other nutrients which may cause additional limitation to above-ground production once N limitation is alleviated.
Do insectivorous bird communities decline on land-bridge forest islands in Peninsular Malaysia?
Authors: Yong Ding Li , Qie Lan , Sodhi Navjot S. , Koh Lian Pin , Peh Kelvin S.-H. , Lee Tien Ming , Lim Haw Chuan , Lim Susan L.-H.
Published: January 2011

To assess the impact of habitat fragmentation on tropical avian communities, we sampled lowland forest birds on six land-bridge islands and two mainland forest sites in Lake Kenyir, Peninsular Malaysia using timed point counts, hypothesizing that insectivorous birds are the worst affected guild. We used an information-theoretic approach to evaluate the effects of area, isolation, primary dietary guild (omnivore, frugivore and insectivore) and their interactions in predicting species richness, abundance and diversity. Our analysis showed that a model that considered the effects of area, dietary guild and their interaction best explained observed patterns of species richness. But a model considering both area and dietary guild best explained the variation in abundance. Notably, insectivorous birds were singled out as the dietary guild most sensitive to fragmentation, followed by frugivorous and omnivorous birds and hence provide support for our hypothesis. Assemblages of insectivorous birds were clearly depauperate on anthropogenic forest islands in Lake Kenyir and are consistent with forest fragmentation studies in the Neotropics. Given their specialized foraging ecology and diversity, conservation of intact communities of insectivorous bird guilds in Malaysia will be critical for maintaining predator–prey interactions in lowland tropical forests.
The plant-ant Camponotus schmitzi helps its carnivorous host-plant Nepenthes bicalcarata to catch its prey
Authors: Bonhomme Vincent , Gounand Isabelle , Alaux Christine , Jousselin Emmanuelle , Barthélémy Daniel , Gaume Laurence
Published: January 2011

The Bornean climber, Nepenthes bicalcarata, is unique among plants because it is both carnivorous and myrmecophytic, bearing pitcher-shaped leaves and the ant Camponotus schmitzi within tendrils. We explored, in the peat swamp forests of Brunei, the hypothesis that these ants contribute to plant nutrition by catching and digesting its prey. We first tested whether ants increased plant's capture rate. We found that unlike most plant-ants, C. schmitzi do not exhibit dissuasive leaf-patrolling behaviour (zero patrol on 67 pitchers of 10 plants) but lie concealed under pitcher rim (13 ± 6 ants per pitcher) allowing numerous insect visits. However, 47 out of 50 individuals of the largest visitor dropped into the pitchers of five plants were attacked by ants and the capture rate of the same pitchers deprived of their ambush hunting ants decreased three-fold. We then tested whether ants participated in plant's digestion. We showed in a 15-d long experiment that ants fed on prey and returned it in pieces in seven out of eight pitchers. The 40 prey deposited in ant-deprived pitchers remained intact indicating a weak digestive power of the fluid confirmed to be only weakly acidic (pH ~5, n = 67). The analysis of 10 pitcher contents revealed that prey, mainly ants and termites, was very numerous (~400 per pitcher per plant) and highly fragmented. Altogether, these data suggest a positive effect of C. schmitzi on both prey intake and breakdown. This ant–plant interaction could thus be a nutritional mutualism involving the unusual association of carnivory and myrmecotrophy.
Effects of forest fragmentation on assemblages of pollinators and floral visitors to male- and female-phase inflorescences of Astrocaryum mexicanum (Arecaceae) in a Mexican rain forest
Authors: Aguirre Armando , Guevara Roger , Dirzo Rodolfo
Published: January 2011

We examined the consequences of habitat fragmentation on the assemblage of floral visitors and pollinators to male- and female-phase inflorescences of the understorey dominant palm Astrocaryum mexicanum at the Los Tuxtlas tropical rain forest. In six forest fragments ranging from 2 to 700 ha, we collected all floral visitors, pollinators and non-pollinators, to male- and female-phase inflorescences at the time of their greatest activity. We used multivariate and mixed-effects models to explore differences in guild composition between sexual phases of inflorescences and the effects of forest fragment size on several metrics of the assemblages of floral visitors. We detected 228 786 floral visitors, grouped into 57 species, across the six forest fragments. On average, abundance and species richness of floral visitors to female-phase inflorescences were higher than to male-phase ones. Forest fragmentation had no effect on species richness but negatively affected Shannon's diversity index. Overall, the most abundant species of floral visitors were predominantly found in inflorescences of plants from the large fragments. In contrast, most of the less common species were more abundant in the smallest fragments. The abundance of pollinators (those found on inflorescences of both phases and dusted with pollen that was carried to flower stigmas), and the ratio of pollinators to other floral visitors, increased with fragment size in both sexual phases of the inflorescences but these effects were significantly stronger on male-phase inflorescences than on female-phase inflorescences. These results show that tropical forest fragmentation correlates with changes in the composition of flower visitors to a dominant palm, with a reduction in the abundance of pollinators, but that such changes co-vary with the sexual phase of the plants.
Fire favours expansion of bamboo-dominated forests in the south-west Amazon
Authors: Smith Maira , Nelson Bruce Walker
Published: January 2011

Forests dominated by semi-scandent woody bamboos of the genusGuaduacover about 165 000 km2of the south-west Amazon. Because many woody bamboo species are favoured by disturbance some authors have inferred this landscape to be a consequence of indigenous or natural disturbance. As seen in satellite images, the rounded edges of some bamboo-dominated forests indicate expansion into surrounding forest. These edges are unrelated to topography and resemble the borders of ground fires in unlogged Amazon forests, suggesting that bamboo may have been favoured by past fires. We studied the recovery ofGuadua sarcocarpaand its competitors in the face of simulated fire by cutting all plant stems at ground level in ten 100-m2plots, compared with ten control plots, and by burning a 2500-m2plot. In the clear-cuts, bamboos recovered more successfully than did palms and dicots, by two measures: biomass accumulated and per cent recovery of pre-disturbance biomass. Resprouted bamboo attained higher stem densities than in control sites at 11 mo. In the burn plot, bamboo basal area recovered to pre-burn levels after 2 y and approached that of an undisturbed control area after 3 y. Though other natural disturbances are relevant, we conclude that forest fires should favour the spread and dominance ofGuaduaspecies in the south-west Amazon.
Seed comas of bromeliads promote germination and early seedling growth by wick-like water uptake
Authors: Wester Stefan , Zotz Gerhard
Published: January 2011

The wind dispersal of a plant propagule is likely to be improved by any structure that increases air resistance, e.g. the pappus of the achene of Asteraceae, the wings ofAceror dipterocarp fruits, or the plumose seed appendage which is characteristic of species of the subfamily Tillandsioideae in the Bromeliaceae. Not surprisingly then, promotion of airworthiness is usually assumed to be the primary function of this so-called ‘coma’ found in epiphyticWerauhia,Tillandsia,GuzmaniaorCatopsisspecies (Benzing 1980, 2000). However, the diverse structure of coma hairs with bifurcate cross-walls or hooks also assists in sticking to rough surfaces, such as tree bark and rocks, which indicates another important function: keeping seeds in place until germination and the development of roots (Benzing 2000, Palacíet al. 2004). Multiple rather than singular functions of seed plumes or pappi have also been shown for soil-rooted plants in other plant families, where these structures are not only highly efficient for wind dispersal, but also for attachment to animal fur (Couvreuret al. 2004).
Successional trends in soil seed banks of abandoned pastures of a Neotropical dry region
Authors: Maza-Villalobos Susana , Lemus-Herrera Celina , Martínez-Ramos Miguel
Published: January 2011

A chronosequence was used to study seed-bank communities during the first 12 y of tropical-dry-forest regeneration in abandoned pastures in Chamela, Mexico. Prediction that seeds of woody species replace those of herbaceous species during succession was tested and mechanisms of species replacement (facilitation, tolerance, inhibition) were assessed. Four successional categories (three sites each) were considered: pasture (0–1 y since abandonment), early (3–5 y), intermediate (10–12 y), and old-growth forest. At the end of the dry season, 20 cylindrical soil samples (10 cm diameter, 15 cm depth) were randomly obtained within a 20 × 50-m plot in each site. Seeds ≥1 mm were counted and identified. Overall, 2941 seeds and 102 morphospecies (52 taxonomically identified) were recorded. Seed bank density reduced, species diversity remained fairly constant and seeds of herbaceous species were replaced by those of woody species over the chronosequence. A clear species-by-species replacement pattern was detected, as expected under a mechanism of succession by facilitation. Twelve years after abandonment, a diverse seed bank of woody species did exist, indicating a fast recovery of the tropical-dry-forest regenerative potential; nonetheless, the structure and composition of the seed bank was still different from that in the old-growth forest.
Progress in research on dry afterripening
Authors: Iglesias-Fernández Raquel , del Carmen Rodríguez-Gacio María , Matilla Angel J.
Published: January 2011

The transition from the dormant to the non-dormant state of a viable and mature seed can take place at low hydration by exposure to air-dry storage conditions (dry afterripening; AR). The events occurring during this loss of dormancy are of considerable physiological, ecological and agricultural interest. AR may be attributable to increased sensitivity to germination-stimulating factors and a widening of the temperature window for germination. Genetic, –omics and physiological studies on this mode of dormancy breaking provide support for a key role of the balance between gibberellin (GA) and abscisic acid (ABA) metabolism and sensitivity. Recent evidence also supports a possible role for ethylene (ET) in this complex signalling network that is necessary for AR implementation. However, hormone-independent signals, such as reactive oxygen species (ROS), nitrate (NO _{3}^{ - }) or nicotinamide adenine dinucleotide (NAD+), also appear to be involved. The way in which hormone- and non-hormone-signalling pathways affects each other (cross-talk) is still under study. This review provides updated information on the programmes that overcome seed dormancy. Thus, we have reviewed: (1) the –omic status in dry seeds; (2) the relationship between temperature and nitrate signalling and AR; (3) alterations in ABA/GA synthesis and signalling; (4) the action of hormone molecules other than ABA and GA (i.e. ET, salicylic and jasmonic acids); and (5) participation of reactive oxygen species (ROS), NAD+and protein carbonylation. Taken together, the acquisition and implementation of dry AR involve a complex signalling network that is difficult to disentangle.
Executive Function Profiles of Pedophilic and Nonpedophilic Child Molesters
Authors: Eastvold Angela , Suchy Yana , Strassberg Donald
Published: January 2011

There is increasing evidence of neurocognitive dysfunction among child molesters, supporting the notion of brain anomalies among pedophiles. However, approximately half of child molesters are not pedophilic (i.e., are not primarily attracted to children), and neurocognitive differences between pedophilic (PED) and nonpedophilic (NPED) child molesters are not well understood. The purpose of this study was to assess neurocognition, specifically executive functioning (EF), among phallometrically defined PED and NPED child molesters, relative to nonsexual offenders (NSO). Participants (N = 89) were compared on seven EF domains. Results revealed that (a) child molesters exhibited an overall executive profile that was different from that of NSOs, with PEDs differing from NSOs but not from NPEDs; (b) child molesters on the whole performed better than NSOs on abstract reasoning and more poorly on inhibition; and (c) PEDs performed better than NPEDs on planning and exhibited better overall performance accuracy relative to NPEDs. These results suggest that PEDs exhibit a more deliberate, planful response style characterized by greater self-monitoring; whereas NPEDs appear to respond more impulsively. The current report further elucidates neurocognition among child molesters and highlights the need for future research examining subtypes of child molesters. (JINS, 2011, 17, 295–307)
Metagenomics of the subsurface Brazos-Trinity Basin (IODP site 1320): comparison with other sediment and pyrosequenced metagenomes
Authors: Biddle Jennifer F , White James Robert , Teske Andreas P , House Christopher H
Published: January 2011

The Brazos-Trinity Basin on the slope of the Gulf of Mexico passive margin was drilled during Integrated Ocean Drilling Progam Expedition 308. The buried anaerobic sediments of this basin are largely organic-poor and have few microbial inhabitants compared with the organic-rich sediments with high cell counts from the Peru Margin that were drilled during Ocean Drilling Program Leg 201. Nucleic acids were extracted from Brazos-Trinity Basin sediments and were subjected to whole-genome amplification and pyrosequencing. A comparison of the Brazos-Trinity Basin metagenome, consisting of 105 Mbp, and the existing Peru Margin metagenome revealed trends linking gene content, phylogenetic content, geological location and geochemical regime. The major microbial groups (Proteobacteria, Firmicutes, Euryarchaeota and Chloroflexi) occur consistently throughout all samples, yet their shifting abundances allow for discrimination between samples. The cluster of orthologous groups category abundances for some classes of genes are correlated with geochemical factors, such as the level of ammonia. Here we describe the sediment metagenome from the oligotrophic Brazos-Trinity Basin (Site 1320) and show similarities and differences with the dataset from the Pacific Peru Margin (Site 1229) and other pyrosequenced datasets. The microbial community found at Integrated Ocean Drilling Program Site 1320 likely represents the subsurface microbial inhabitants of turbiditic slopes that lack substantial upwelling.
Solvent effect on the absorption spectra of coumarin 120 in water: A combined quantum mechanical and molecular mechanical study
Authors: Sakata Tetsuya , Kawashima Yukio , Nakano Haruyuki
Published: January 2011

The solvent effect on the absorption spectra of coumarin 120 (C120) in water was studied utilizing the combined quantum mechanical/molecular mechanical (QM/MM) method. In molecular dynamics (MD) simulation, a new sampling scheme was introduced to provide enough samples for both solute and solvent molecules to obtain the average physical properties of the molecules in solution. We sampled the structure of the solute and solvent molecules separately. First, we executed a QM/MM MD simulation, where we sampled the solute molecule in solution. Next, we chose random solute structures from this simulation and performed classical MD simulation for each chosen solute structure with its geometry fixed. This new scheme allowed us to sample the solute molecule quantum mechanically and sample many solvent structures classically. Excitation energy calculations using the selected samples were carried out by the generalized multiconfigurational perturbation theory. We succeeded in constructing the absorption spectra and realizing the red shift of the absorption spectra found in polar solvents. To understand the motion of C120 in water, we carried out principal component analysis and found that the motion of the methyl group made the largest contribution and the motion of the amino group the second largest. The solvent effect on the absorption spectrum was studied by decomposing it in two components: the effect from the distortion of the solute molecule and the field effect from the solvent molecules. The solvent effect from the solvent molecules shows large contribution to the solvent shift of the peak of the absorption spectrum, while the solvent effect from the solute molecule shows no contribution. The solvent effect from the solute molecule mainly contributes to the broadening of the absorption spectrum. In the solvent effect, the variation in C–C bond length has the largest contribution on the absorption spectrum from the solute molecule. For the solvent effect on the absorption spectrum from the solvent molecules, the solvent structure around the amino group of C120 plays the key role.
Putting the squeeze on cavities in liquids: Quantifying pressure effects on solvation using simulations and scaled-particle theory
Authors: Ashbaugh Henry S. , Truskett Thomas M.
Published: January 2011

Extensive molecular simulations of the Lennard-Jones fluid are performed to examine the response of the excess chemical potential of cavitylike solutes to applied pressure. Solutes as large as ten times the solvent diameter are considered. The simulations are analyzed using the revised scaled-particle theory developed by Ashbaugh and Pratt to evaluate the thermodynamics of cavity solvation and curvature dependent interfacial properties well into the compressed liquid portion of the solvent phase diagram. The revised theory provides a quantitatively accurate description of the solvent–solute contact correlation function for all solutes and state points considered. The main structural effect of increasing pressure is to push the solvent molecules up against the solute surfaces, counteracting the dewetting that is observed at lower pressures along the solvent saturation curve. Decomposing the excess chemical potential of cavities into volume and surface-area contributions shows that pressure differentially affects the interfacial free energies of molecular versus macroscopic solutes. The interfacial free energy of surfaces of molecular dimension monotonically decreases with applied pressure, while that of surfaces larger than a small cluster of solvent molecules exhibit a maximum with increasing pressure, which may play a role in pressure-induced disaggregation of molecular assemblies. Moreover, since the pressure dependence of the interfacial free energy is thermodynamically linked to the excess adsorption of solvent on the solute surface, the former is potentially a measurable macroscopic indicator of microscopic wetting/dewetting phenomena, implicated in hydrophobic interactions between macroscopic hydrophobic particles. Finally, some inferences about pressure-dependent solvation processes in water are made by using the revised theory to analyze previously published simulation data.
Full-dimensional quantum dynamics calculations of H2–H2 collisions
Authors: Balakrishnan N. , Quéméner G. , Forrey R. C. , Hinde R. J. , Stancil P. C.
Published: January 2011

We report quantum dynamics calculations of rotational and vibrational energy transfer in collisions between two para-H \documentclass[12pt]{minimal}\begin{document}$_2$\end{document}2 molecules over collision energies spanning from the ultracold limit to thermal energies. Results obtained using a recent full-dimensional \documentclass[12pt]{minimal}\begin{document}${\rm H}_2$\end{document}H2–H \documentclass[12pt]{minimal}\begin{document}$_2$\end{document}2 potential energy surface (PES) developed by Hinde [J. Chem. Phys. 128, 154308 (2008)] are compared with those derived from the Boothroyd, Martin, Keogh, and Peterson (BMKP) PES [J. Chem. Phys. 116, 666 (2002)]. For vibrational relaxation of \documentclass[12pt]{minimal}\begin{document}${\rm H}_2(v=1,j=0)$\end{document}H2(v=1,j=0) by collisions with H \documentclass[12pt]{minimal}\begin{document}$_2(v=0,j=0)$\end{document}2(v=0,j=0) as well as rotational excitations in collisions between ground state \documentclass[12pt]{minimal}\begin{document}${\rm H}_2$\end{document}H2 molecules, the PES of Hinde is found to yield results in better agreement with available experimental data. A highly efficient near-resonant energy transfer mechanism that conserves internal rotational angular momentum and was identified in our previous study of the \documentclass[12pt]{minimal}\begin{document}${\rm H}_2\hbox{–}{\rm H}_2$\end{document}H2–H2 system [Phys. Rev. A 77, 030704(R) (2008)] using the BMKP PES is also found to be reproduced by the Hinde PES, demonstrating that the process is largely insensitive to the details of the PES. In the absence of the near-resonance mechanism, vibrational relaxation is driven by the anisotropy of the potential energy surface. Based on a comparison of results obtained using the Hinde and BMKP PESs with available experimental data, it appears that the Hinde PES provides a more accurate description of rotational and vibrational transitions in \documentclass[12pt]{minimal}\begin{document}${\rm H}_2$\end{document}H2–H \documentclass[12pt]{minimal}\begin{document}$_2$\end{document}2 collisions, at least for vibrational quantum numbers v ⩽ 1.
A quantitative analysis of room temperature recrystallization kinetics in electroplated copper films using high resolution x-ray diffraction
Authors: Ying Andrew , Witt Christian , Jordan-Sweet Jean , Rosenberg Robert , Noyan I. C.
Published: January 2011

Time-resolved in situ x-ray diffraction measurements were used to study the room-temperature recrystallization kinetics of electroplated copper thin films with thicknesses between 400 and 1000 nm. The thinnest films exhibited limited recrystallization and subsequent growth of grains, while recrystallized grains in the thicker films grew until all as-plated microstructure was consumed. For all films, recrystallized grains that belonged to the majority texture component, ⟨111⟩, started growing after the shortest incubation time. These grains exhibited volumetric growth until they achieved the film thickness. After this point the growth mode became planar, with the ⟨111⟩-type grains growing in the plane of the film. Grains with the ⟨100⟩ direction normal to the film surface started growing after the ⟨111⟩-type grains switched to planar growth. However, the planar growth of this texture component finished at the same time as the growth of the ⟨111⟩ grains. Profile fitting of the 111 peak permitted the separation of the diffraction signals from recrystallized and as-plated grain populations. The average strains in these two populations, calculated from the peak position of the corresponding {111} reflections, were different, indicating a heterogeneous stress state within this texture component. The increasing volume fraction of recrystallized ⟨111⟩ grains with time was monitored via the variation in the diffracted intensity. This variation could be represented by the Johnson–Mehl–Avrami–Kolmogorov model.
Resonant Raman spectra of diindenoperylene thin films
Authors: Scholz R. , Gisslén L. , Schuster B.-E. , Casu M. B. , Chassé T. , Heinemeyer U. , Schreiber F.
Published: January 2011

Resonant and preresonant Raman spectra obtained on diindenoperylene (DIP) thin films are interpreted with calculations of the deformation of a relaxed excited molecule with density functional theory (DFT). The comparison of excited state geometries based on time-dependent DFT or on a constrained DFT scheme with observed absorption spectra of dissolved DIP reveals that the deformation pattern deduced from constrained DFT is more reliable. Most observed Raman peaks can be assigned to calculated \documentclass[12pt]{minimal}\begin{document}$A_g$\end{document}Ag-symmetric breathing modes of DIP or their combinations. As the position of one of the laser lines used falls into a highly structured absorption band, we have carefully analyzed the Raman excitation profile arising from the frequency dependence of the dielectric tensor. This procedure gives Raman cross sections in good agreement with the observed relative intensities, both in the fully resonant and in the preresonant case.
Infrared spectroscopy of Sc+(H2O) and Sc2+(H2O) via argon complex predissociation: The charge dependence of cation hydration
Authors: Carnegie P. D. , Bandyopadhyay B. , Duncan M. A.
Published: January 2011

Singly and doubly charged scandium–water ion-molecule complexes are produced in a supersonic molecular beam by laser vaporization. These ions are mass analyzed and size selected in a specially designed reflectron time-of-flight spectrometer. To probe their structure, vibrational spectroscopy is measured for these complexes in the O–H stretching region using infrared laser photodissociation and the method of rare gas atom predissociation, also known as “tagging.” The O–H stretches in these systems are shifted to lower frequency than those for the free water molecule, and the intensity of the symmetric stretch band is strongly enhanced relative to the asymmetric stretch. These effects are more prominent for the doubly charged ions. Partially resolved rotational structure for the Sc+(H2O)Ar complex shows that the H–O–H bond angle is larger than it is in the free water molecule. Fragmentation and spectral patterns indicate that the coordination of the Sc2+ ion is filled with six ligands (one water and five argons).
Local formation of a Heusler structure in CoFe–Al alloys
Authors: Wurmehl S. , Jacobs P. J. , Kohlhepp J. T. , Swagten H. J. M. , Koopmans B. , Maat S. , Carey M. J. , Childress J. R.
Published: January 2011

We systematically study the changes in the local atomic environments of Co in CoFe–Al alloys as a function of Al content by means of nuclear magnetic resonance. We find that a Co2FeAl Heusler type structure is formed on a local scale. The observed formation of a highly spin-polarized Heusler compound may explain the improved magnetotransport properties in CoFe–Al based current-perpendicular-to-the-plane spin-valves.
Hydrogen-graphite interaction: Experimental evidences of an adsorption barrier
Authors: Aréou E. , Cartry G. , Layet J.-M. , Angot T.
Published: January 2011

The interaction of H atoms having relatively low average kinetic energy (∼0.025 eV) with both perfectly clean and D-covered HOPG surfaces is investigated using high resolution electron energy loss spectroscopy. From this study we confirm, in a controlled fashion, the presence of the theoretically predicted adsorption barrier since no adsorption is detected for such H atoms on HOPG. Moreover, we demonstrate that the exposure of a D saturated HOPG surface to these H atoms results in the complete removal of adatoms, with no further adsorption despite the prediction of the adsorption barrier to vanish for H dimers in para configuration. Therefore, the recombinative abstraction mechanism which competes with the adsorption process is more efficient.
Excess entropy scaling of transport properties in network-forming ionic melts (SiO $_2$2 and BeF $_2$2)
Authors: Agarwal Manish , Singh Murari , Shadrack Jabes B. , Chakravarty Charusita
Published: January 2011

The regime of validity of Rosenfeld excess entropy scaling of diffusivity and viscosity is examined for two tetrahedral, network-forming ionic melts (BeF \documentclass[12pt]{minimal}\begin{document}$_2$\end{document}2 and SiO \documentclass[12pt]{minimal}\begin{document}$_2$\end{document}2) using molecular dynamics simulations. With decrease in temperature, onset of local caging behavior in the diffusional dynamics is shown to be accompanied by a significant increase in the effect of three-body and higher-order particle correlations on the excess entropy, diffusivity, ionic conductivity, and entropy-transport relationships. The signature of caging effects on the Rosenfeld entropy scaling of transport properties is a distinctly steeper dependence of the logarithm of the diffusivity on the excess entropy in ionic melts. This is shown to be true also for a binary Lennard-Jones glassformer, based on available results in the literature. Our results suggest that the onset of a landscape-influenced regime in the dynamics is correlated with this characteristic departure from Rosenfeld scaling. The breakdown of the Nernst–Einstein relation in the ionic melts can also be correlated with the emerging cooperative dynamics.
A comparative study of TiN and TiC: Oxidation resistance and retention of xenon at high temperature and under degraded vacuum
Authors: Gavarini S. , Bes R. , Millard-Pinard N. , Cardinal S. , Peaucelle C. , Perrat-Mabilon A. , Garnier V. , Gaillard C.
Published: January 2011

Dense TiN and TiC samples were prepared by hot pressing using micrometric powders. Xenon species (simulating rare gas fission products) were then implanted into the ceramics. The samples were annealed for 1 h at 1500 °C under several degraded vacuums with PO2 varying from 10−6 to 2×10−4 mbars. The oxidation resistance of the samples and their retention properties with respect to preimplanted xenon species were analyzed using scanning electron microscopy, grazing incidence x-ray diffraction, Rutherford backscattering spectrometry, and nuclear backscattering spectrometry. Results indicate that TiC is resistant to oxidation and does not release xenon for PO2≤6×10−6 mbars. When PO2 increases, geometric oxide crystallites appear at the surface depending on the orientation and size of TiC grains. These oxide phases are Ti2O3, Ti3O5, and TiO2. Apparition of oxide crystallites is associated with the beginning of xenon release. TiC surface is completely covered by the oxide phases at PO2=2×10−4 mbars up to a depth of 3 μm and the xenon is then completely released. For TiN samples, the results show a progressive apparition of oxide crystallites (Ti3O5 mainly) at the surface when PO2 increases. The presence of the oxide crystallites is also directly correlated with xenon release, the more oxide crystallites are growing the more xenon is released. TiN surface is completely covered by an oxide layer at PO2=2×10−4 mbars up to 1 μm. A correlation between the initial fine microstructure of TiN and the properties of the growing layer is suggested.
Nonuniversality of density and disorder in jammed sphere packings
Authors: Jiao Yang , Stillinger Frank H. , Torquato Salvatore
Published: January 2011

We show for the first time that collectively jammed disordered packings of three-dimensional monodisperse frictionless hard spheres can be produced and tuned using a novel numerical protocol with packing density ϕ as low as 0.6. This is well below the value of 0.64 associated with the maximally random jammed state and entirely unrelated to the ill-defined “random loose packing” state density. Specifically, collectively jammed packings are generated with a very narrow distribution centered at any density ϕ over a wide density range ϕ∊(0.6,0.740 48…) with variable disorder. Our results support the view that there is no universal jamming point that is distinguishable based on the packing density and frequency of occurrence. Our jammed packings are mapped onto a density-order-metric plane, which provides a broader characterization of packings than density alone. Other packing characteristics, such as the pair correlation function, average contact number, and fraction of rattlers are quantified and discussed.
Competition of compressive strain with substrate misorientation in CuPt-type ordered GaInP/AlGaInP quantum wells
Authors: Zhu Liangqing , Shao Jun , Lü Xiang , Guo Shaoling , Chu Junhao
Published: January 2011

Temperature-dependent photoluminescence (PL) measurements are carried out on lattice-matched and compressively strained GaxIn1−xP/(Al0.66Ga0.34)yIn1−yP quantum wells (QWs) with CuPt-type long-range (LR) ordering. Experimental data show that compressive strain and substrate misorientation of the QWs affect the degree of LR ordering. The compressive strain competes with the misorientation of 6° off toward [111]A (denoted as 6 °A) significantly. It not only affects the distribution of domains with different degree of LR ordering in the x−y plane but also introduces fluctuation of the degree of LR ordering along the z direction of the QWs, which in turn causes the splitting of PL peaks. A phenomenological model is proposed to account for the experimental phenomena based on the principle of minimum total free energy. The results suggest that 6 °A misorientation should not be preferable for compressively strained GaxIn1−xP QWs with LR ordering.
Wide band gap tunability of bulk Cd1−xCaxO
Authors: Srihari Velaga , Sridharan V. , Chandra Sharat , Sastry V. S. , Sahu H. K. , Sundar C. S.
Published: January 2011

We report the lattice parameter variation and the band gap tuning of CdO with Ca by preparing thermodynamically stable Cd1−xCaxO solid solution in the entire composition range 0≤x≤1. The functional dependence of the lattice parameter on Ca concentration is found to deviate from Vegard’s law. The principal band gap is found to vary nonmonotonically over a wide range, from 1.4 to 3.9 eV for 0≤x≤0.8. First principles density functional theory calculations, using full potential linearized augmented plane wave methods also predict a nonlinear variation for the lattice parameter and the optical band gap with Ca concentration. From these calculations, contributions from volume deformation, electron transfer, and structural relaxation are estimated and the results are compared with experiments.
Measurement of valence-band offsets of InAlN/GaN heterostructures grown by metal-organic vapor phase epitaxy
Authors: Akazawa M. , Gao B. , Hashizume T. , Hiroki M. , Yamahata S. , Shigekawa N.
Published: January 2011

The valence band offsets, ΔEV, of In0.17Al0.83N/GaN, In0.25Al0.75N/GaN, and In0.30Al0.70N/GaN heterostructures grown by metal-organic vapor phase epitaxy were evaluated by using x-ray photoelectron spectroscopy (XPS). The dependence of the energy position and the full width at half maximum of the Al 2p spectrum on the exit angle indicated that there was sharp band bending caused by the polarization-induced electric field combined with surface Fermi-level pinning in each ultrathin InAlN layer. The ΔEV values evaluated without taking into account band bending indicated large discrepancies from the theoretical estimates for all samples. Erroneous results due to band bending were corrected by applying numerical calculations, which led to acceptable results. The evaluated ΔEV values were 0.2±0.2 eV for In0.17Al0.83N/GaN, 0.1±0.2 eV for In0.25Al0.75N/GaN, and 0.0±0.2 eV for In0.30Al0.70N/GaN. Despite the large decrease of around 1.0 eV in the band gap of InAlN layers according to the increase in the In molar fraction, the decrease in ΔEV was as small as 0.2 eV. Therefore, the change in band-gap discontinuity was mainly distributed to that in conduction band offset.
Observation of negative capacitances in Al/P(VDF-TrFE)/SiO2/nSi structures
Authors: Tadros-Morgane Raphael , Vizdrik Gennady , Martin Bjoern , Kliem Herbert
Published: January 2011

Metal-insulator-semiconductor structures with thin films of the ferroelectric copolymer poly(vinylidene fluoride trifluoroethylene) on oxidized n-silicon exhibit negative capacitances, i.e., inductivelike behavior. The magnitude of negative capacitances depends besides on the layer properties also on frequency and bias. Additional time domain measurements confirm the inductive character. A qualitative model for this behavior based on space charge limited currents is briefly discussed.
Microdischarge extreme ultraviolet source with alkali metal vapor for surface morphology application
Authors: Higashiguchi Takeshi , Terauchi Hiromitsu , Otsuka Takamitsu , Yamaguchi Mami , Kikuchi Keisuke , Yugami Noboru , Yatagai Toyohiko , Sasaki Wataru , D’Arcy Rebekah , Dunne Padraig , O’Sullivan Gerry
Published: January 2011

We have characterized a discharge-produced potassium plasma extreme ultraviolet (XUV) source. Potassium ions produced strong broadband emission around 40 nm with a bandwidth of 8 nm (full width at half-maximum). By comparison with atomic structure calculations, the broadband emission is found to be primarily due to 3d–3p transitions in potassium ions ranging from K2+ to K4+. The current-voltage characteristics of the microdischarge suggest that the source operates in a hollow cathode mode and consequently the emitting ions may be localized on the potassium electrode surface at the hole into the capillary. To understand the spectral behavior from the potassium plasmas we compared the spectra from the discharge-produced plasma with that from a laser-produced plasma. The spectra from the different (electric and laser) plasmas at the same electron temperature (12 eV) were almost the same. This compact capillary XUV source with a photon energy of 30 eV is a useful XUV emission source for surface morphology applications.
A fundamental measure theory for the sticky hard sphere fluid
Authors: Hansen-Goos Hendrik , Wettlaufer J. S.
Published: January 2011

We construct a density functional theory (DFT) for the sticky hard sphere (SHS) fluid which, like Rosenfeld's fundamental measure theory (FMT) for the hard sphere fluid [Y. Rosenfeld, Phys. Rev. Lett. 63, 980 (1989)], is based on a set of weighted densities and an exact result from scaled particle theory (SPT). It is demonstrated that the excess free energy density of the inhomogeneous SHS fluid \documentclass[12pt]{minimal}\begin{document}$\Phi _{{\rm SHS}}$\end{document}Φ SHS is uniquely defined when (a) it is solely a function of the weighted densities from Kierlik and Rosinberg's version of FMT [E. Kierlik and M. L. Rosinberg, Phys. Rev. A 42, 3382 (1990)], (b) it satisfies the SPT differential equation, and (c) it yields any given direct correlation function (DCF) from the class of generalized Percus–Yevick closures introduced by Gazzillo and Giacometti [J. Chem. Phys. 120, 4742 (2004)]. The resulting DFT is shown to be in very good agreement with simulation data. In particular, this FMT yields the correct contact value of the density profiles with no adjustable parameters. Rather than requiring higher order DCFs, such as perturbative DFTs, our SHS FMT produces them. Interestingly, although equivalent to Kierlik and Rosinberg's FMT in the case of hard spheres, the set of weighted densities used for Rosenfeld's original FMT is insufficient for constructing a DFT which yields the SHS DCF.
Flow past two rotating cylinders
Authors: Kumar S. , Gonzalez B. , Probst O.
Published: January 2011

Flow past two uniformly rotating cylinders with the same rotation rates in a side-by-side configuration is studied experimentally. The experiments are carried out at Reynolds numbers, Re, of 100, 200, 300, 400, and 500 and nondimensional rotation rates, α, varying from 0 to 5. The spacing ratios, T/D, are 1.8, 2.5, 4.0, and 7.5. Two possibilities of rotations are considered with the cylinder surfaces in between the two cylinders moving upstream in one case (inward rotation case) and downstream in the other (outward rotation case). The diagnostics is done by flow visualization using hydrogen bubble technique and quantitative measurements using particle image velocimetry (PIV). We present, using extensive flow visualization, the global view of the wake structure at Re of 200 for various rotation rates, and two senses. Vortex shedding suppression is studied through flow visualization and/or PIV at various Re’s, T/D’s, and two senses. Vortex shedding is found to be suppressed in the inward rotation cases at all Re and T/D’s. The value of α corresponding to vortex shedding suppression, αs, in the inward rotation case is ∼2.0 for Re of 200–500 at all T/D’s. The value of αs for Re of 100 in the case of inward rotation shows an increasing trend with T/D from T/D=1.8 to 4.0 with αs changing from 1.2 to 1.7; further increase of T/D does not change αs. For outward rotation cases, vortex shedding suppression is clearly observed for Re of 100 and for all values of T/D; however, for higher Re, vortex shedding suppression is observed for T/D of 4.0 and 7.5 only. The measurements of αs in this case showed a decreasing trend with increasing T/D. Symmetry breaking is reported for inward rotation case near α=1.35 for T/D=2.5 at Re of 200 where the wake pattern changes from in-phase to antiphase mode.
A wall-layer model for large-eddy simulations of turbulent flows with/out pressure gradient
Authors: Duprat C. , Balarac G. , Métais O. , Congedo P. M. , Brugière O.
Published: January 2011

In this work, modeling of the near-wall region in turbulent flows is addressed. A new wall-layer model is proposed with the goal to perform high-Reynolds number large-eddy simulations of wall bounded flows in the presence of a streamwise pressure gradient. The model applies both in the viscous sublayer and in the inertial region, without any parameter to switch from one region to the other. An analytical expression for the velocity field as a function of the distance from the wall is derived from the simplified thin-boundary equations and by using a turbulent eddy coefficient with a damping function. This damping function relies on a modified van Driest formula to define the mixing-length taking into account the presence of a streamwise pressure gradient. The model is first validated by a priori comparisons with direct numerical simulation data of various flows with and without streamwise pressure gradient and with eventual flow separation. Large-eddy simulations are then performed using the present wall model as wall boundary condition. A plane channel flow and the flow over a periodic arrangement of hills are successively considered. The present model predictions are compared with those obtained using the wall models previously proposed by Spalding, Trans. ASME, J. Appl. Mech 28, 243 (2008) and Manhart et al., Theor. Comput. Fluid Dyn. 22, 243 (2008). It is shown that the new wall model allows for a good prediction of the mean velocity profile both with and without streamwise pressure gradient. It is shown than, conversely to the previous models, the present model is able to predict flow separation even when a very coarse grid is used.
Adsorbate-localized states at water-covered (100) SrTiO3 surfaces
Authors: Raghavan S. , Carvalho A. , Le Formal F. , Setter N. , Öberg S. , Briddon P. R.
Published: January 2011

The electronic structure of hydrated SrTiO3 (001) surfaces is investigated using density-functional models. It is shown that adsorbed water molecules give rise to unoccupied electron states similar in localization and shape to wet-electron states recently reported for other oxide-water interfaces, and believed to serve as a preferred path for transfer of conduction electrons to the surface water molecules. Additionally, we found that chemisorbed water and hydrogen have donor levels in the band gap, and that chemisorbed hydrogen is oxidized and released in the presence of free holes. These gap states can serve as surface recombination centers in photoelectrochemical cells.
Transient studies on InAs/HfO2 nanowire capacitors
Authors: Astromskas Gvidas , Storm Kristian , Wernersson Lars-Erik
Published: January 2011

Single-shot transients and deep-level transient spectroscopy are used to investigate the origins of capacitance hysteresis in n-doped InAs nanowire/HfO2 capacitors. Capacitance transients with a characteristic time in the order of 100 μs are attributed to emission from electron traps, located in the oxide film. The trap energy is determined to be in the range from 0.12 to 0.17 eV with capture cross-sections of about 1.7×10−17 cm−2. The capture is measured to be shorter than 100 ns with no sign of capture barrier. Under the reverse bias, the transients show a reduced emission rate indicating a minority carrier assisted complex dynamics.
Energy level alignment, electron injection, and charge recombination characteristics in CdS/CdSe cosensitized TiO2 photoelectrode
Authors: Chi Ching-Fa , Cho Hsun-Wei , Teng Hsisheng , Chuang Cho-Ying , Chang Yu-Ming , Hsu Yao-Jane , Lee Yuh-Lang
Published: January 2011

The band-edge levels of CdS-, CdSe-, and CdS/CdSe-sensitized TiO2 electrodes were determined by ultraviolet photoelectron spectroscopy (UPS) to explore the reason leading to the high performance of the TiO2/CdS/CdSe electrode. The obtained UPS results show the stepwise energy level in the TiO2/CdS/CdSe electrode, indicating energy level alignment occurrence between CdS and CdSe in the TiO2/CdS/CdSe. Time-resolved photoluminescence and open-circuit photovoltage decay experiments reveal that the photogenerated electrons in the TiO2/CdS/CdSe have higher injection efficiency, but lower recombination rate to the electrolyte, attributable to the stepwise structure of band-edge levels constructed by the effect of the energy level alignment.