bluuebunny/crossref_metadata_2025 huggingface dataset:
Correlated anomalous diffusion: Random walk and Langevin equation
Authors: Sogo Kiyoshi , Kishikawa Yoshiaki , Ohnishi Shuhei , Yamamoto Takenori , Fujiwara Susumu , Aoki Keiko M.
Published: March 2010

A random walk model is formulated and examined which gives the correlated anomalous diffusion found in molecular dynamics simulations. The mean square displacement (MSD) shows a logarithmic behavior in one dimension. Corresponding Langevin equation is constructed by solving the inverse problem which gives a procedure to derive random impulse correlation from MSD function.
Applied spectroscopy in pulsed power plasmas
Authors: Rochau G. A. , Bailey J. E. , Maron Y.
Published: March 2010

Applied spectroscopy is a powerful diagnostic tool for high energy density plasmas produced with modern pulsed power facilities. These facilities create unique plasma environments with a broad range of electron densities (1013–1023 cm−3) and temperatures (100–103 eV) immersed in strong magnetic (>100 T) and electric (up to 1 GV/m) fields. This paper surveys the application of plasma spectroscopy to diagnose a variety of plasma conditions generated by pulsed power sources including: magnetic field penetration into plasma, measuring the time-dependent spatial distribution of 1 GV/m electric fields, opacity measurements approaching stellar interior conditions, characteristics of a radiating shock propagating at 330 km/s, and determination of plasma conditions in imploded capsule cores at 150 Mbar pressures. These applications provide insight into fundamental properties of nature in addition to their importance for addressing challenging pulsed power science problems.
Many-body formulation of carriers capture time in quantum dots applicable in device simulation codes
Authors: Vallone Marco
Published: March 2010

We present an application of Green’s functions formalism to calculate in a simplified but rigorous way electrons and holes capture time in quantum dots in closed form as function of carrier density, levels confinement potential, and temperature. Carrier-carrier (Auger) scattering and single LO-phonon emission are both addressed accounting for dynamic effects of the potential screening in the single plasmon pole approximation of the dielectric function. Regarding the LO-phonons interaction, the formulation evidences the role of the dynamic screening from wetting-layer carriers in comparison with its static limit, describes the interplay between screening and Fermi band filling, and offers simple expressions for capture time, suitable for modeling implementation.
Response-time improved hydrothermal-method-grown ZnO scintillator for soft x-ray free-electron laser timing-observation
Authors: Shimizu Toshihiko , Yamamoi Kohei , Estacio Elmer , Nakazato Tomoharu , Sakai Kouhei , Sarukura Nobuhiko , Ehrentraut Dirk , Fukuda Tsuguo , Nagasono Mitsuru , Togashi Tadashi , Higashiya Atsushi , Yabashi Makina , Ishikawa Tetsuya , Ohashi Haruhiko , Kimura Hiroaki
Published: March 2010

For pump and probe experiments in x-ray free-electron laser (XFEL) facilities, accurate timing synchronization between short-wavelength femtosecond pulses from XFELs and short optical pulses from other light sources is required. For this purpose, the response time of a hydrothermal-method-grown ZnO is improved by over one order of magnitude via intentional iron ion doping. The fluorescence rise- and decay-time constants are measured to be less than 10 and 100 ps, respectively. Owing to its intense fluorescence even for single pulse XFEL excitation, the timing jitter of the soft x-ray pulse and timing electronics are evaluated to be less than 70 ps.
Fixed trace β-Hermite ensembles: Asymptotic eigenvalue density and the edge of the density
Authors: Zhou Da-Sheng , Liu Dang-Zheng , Qian Tao
Published: March 2010

In the present paper, fixed trace β-Hermite ensembles generalizing the fixed trace Gaussian ensembles are considered. For all β, we prove the Wigner semicircle law for these ensembles by using two different methods: one is the moment equivalence method with the help of the matrix model for general β, the other is to use asymptotic analysis tools. At the edge of the density, we prove that the edge scaling limit for β-HE implies the same limit for fixed trace β-Hermite ensembles. Consequently, explicit limit can be given for fixed trace Gaussian orthogonal, unitary, and symplectic ensembles. Furthermore, for even β, analogous to β-Hermite ensembles, a multiple integral of the Konstevich type can be obtained.
Numerical simulations of alternating current loss of high temperature superconductors in the liquid nitrogen region
Authors: Zhao Yu-Feng , He Tian-Hu
Published: March 2010

The frequency f and amplitude B0 of applied magnetic field dependence of the loss behavior in the liquid nitrogen region is studied in high temperature superconducting slabs. The magnetothermal diffusion equations based on the power-law model are presented in this paper to estimate the effect of f and B0 on the loss. Numerical results obtained show that, generally, the loss is proportional to B03 in the nonpenetration field and to B0 in the penetration field, and the loss power is proportional to f whether the magnetic field penetrates it or not.

This article is being retracted effective 12 April 2012.
A new particle interaction mixing model for turbulent dispersion and turbulent reactive flows
Authors: Meyer Daniel W.
Published: March 2010

Probability density function (PDF) methods are an established tool applied for the simulation of turbulent mixing and turbulent reactive flows. Mixing models are required to close the molecular diffusion term in the PDF transport equation. From the nature of molecular diffusion, several requirements or design criteria can be derived for mixing models. All current models have certain shortcomings with respect to these requirements. A new mixing model is presented which fully satisfies almost all requirements. It conserves the mean of an inert scalar, reduces its scalar variance, and relaxes closely to a Gaussian scalar PDF. Multiple inert scalars without differential diffusion effects evolve independently and are kept bounded within their allowable region. Mixing is conditional on the velocity and particle scalar trajectories are continuous in time leading to a model that is local in a weak sense. Validation tests show that the model can reproduce differential diffusion effects and mixing rate dependencies due to variable initial scalar length scales or Reynolds and Schmidt number variations.
Magnetic anisotropy and field switching in cobalt ferrite thin films deposited by pulsed laser ablation
Authors: Dhakal T. , Mukherjee D. , Hyde R. , Mukherjee P. , Phan M. H. , Srikanth H. , Witanachchi S.
Published: March 2010

We report the observation of contrasting magnetic behavior in cobalt ferrite (CFO) thin films deposited on single crystalline magnesium oxide (MgO) and strontium titanate (STO). Epitaxial films on MgO (100) with a lattice mismatch of 0.35% showed out-of-plane anisotropy whereas the films on STO (100) with a lattice mismatch of 7.4% displayed in-plane anisotropy. Stress anisotropy calculated from angle-dependent x-ray diffraction analysis confirmed that the change in anisotropy originates from the lattice mismatch. An additional low-field switching characteristic is observed in the M-H loops of the CFO films, which became prominent with lowering temperature as also evidenced from the rf transverse susceptibility measurements. The obtained results revealed that the low field switching is associated with the film-substrate interface.
Site of incorporation and solubility for Fe ions in acceptor-doped PZT ceramics
Authors: Erdem E. , Eichel R.-A. , Fetzer Cs. , Dézsi I. , Lauterbach S. , Kleebe H.-J. , Balogh A. G.
Published: March 2010

Pb ( Zr 0.54 Ti 0.46 ) O 3 ceramic samples with composition near the morphotropic phase boundary have been investigated. Samples have been nominally doped with 0.5 and 1.0 mol % Fe atoms and studied by electron paramagnetic resonance (EPR), transmission electron microscopy (TEM), and Mössbauer spectroscopy. EPR and Mössbauer measurements indicated the creation of Fe–O vacancy dipoles in the grains and a solubility limit of less than 1 mol % for the Fe atoms in the PZT lattice. TEM studies revealed a dense sample with homogeneous microstructure and a second crystalline phase at the triple pockets with Pb excess. In the case of the 1 mol % Fe:PZT sample, beside the components Pb, Zr, and Ti even Fe was determined in these pockets with higher concentration as in the grains.
Photogated transistor of III-nitride nanorods
Authors: Seo H. W. , Tu L. W. , Chen Q. Y. , Ho C. Y. , Lin Y. T. , Wu K. L. , Jang D. J. , Norman D. P. , Ho N. J.
Published: March 2010

A III-nitride-based photogated transistor using photons to control the channel width of an otherwise gateless field effect transistor (FET) is investigated. This is accomplished by stacking sequential layers of p-GaN/InGaN/n-GaN on a Si substrate in an array of nanorods. The nitride p-i-n diode can be activated by light, whereupon the nanorod device shows phototransistor characteristics in forward bias but behaves like a photoconductor when in reverse bias. An optically pumped FET model, as justified by the low-dimensional nanogeometry, is used in analysis of the device. The resulting photogate efficiency and photocarrier mobilities are estimated to be ∼0.04 V/(W/cm2) and, ∼2000–3000 cm2/V s, respectively.
Equiconducting molecular electronic devices
Authors: Zhou Y. X. , Ernzerhof M.
Published: March 2010

For molecular conductors, the source-sink potential (SSP) model provides a simple tool for the calculation of the electron transmission probability. Recently, the SSP method has been combined with graph theory, and criteria have been established under which two different molecular electronic devices yield identical transmission probabilities. Since these criteria have been arrived at within the Hückel approximation, we investigate the validity of these criteria by performing combined Kohn–Sham and Green’s function calculations for the transmission probability. We find that some systems, predicted to be equiconducting at the Hückel level, are approximately equiconducting at the nonempirical level while others are not. An explanation for the obtained discrepancies is proposed.
Alignment effects on a neutron imaging system using coded apertures
Authors: Thfoin Isabelle , Landoas Olivier , Caillaud Tony , Disdier Laurent , Vincent Maxime , Bourgade Jean-Luc , Rossé Bertrand , Sangster Thomas C. , Glebov Vladimir Yu. , Pien Greg , Armstrong William
Published: March 2010

A high resolution neutron imaging system is being developed and tested on the OMEGA laser facility for inertial confinement fusion experiments. This diagnostic uses a coded imaging technique with a penumbral or an annular aperture. The sensitiveness of these techniques to misalignment was pointed out with both experiments and simulations. Results obtained during OMEGA shots are in good agreement with calculations performed with the Monte Carlo code GEANT4. Both techniques are sensitive to the relative position of the source in the field of view. The penumbral imaging technique then demonstrates to be less sensitive to misalignment compared to the ring. These results show the necessity to develop a neutron imaging diagnostic for megajoule class lasers taking into account our alignment capabilities on such facilities.
Current-voltage characteristics of La2−xSrxCuO4/Nb-doped SrTiO3 heterojunctions
Authors: Yin Y. W. , Ding J. F. , Wang J. , Xie L. , Yu Q. X. , Li X. G.
Published: March 2010

The temperature dependencies of the current-voltage (I-V) characteristics for the La2−xSrxCuO4 (LSCO) (x=0.10, 0.16, and 0.20)/1.0 wt % Nb-doped SrTiO3 (SNTO) heterojunctions were investigated under magnetic fields up to 14 T. The junction resistances for different heterojunctions show remarkable jumps as soon as the superconductivities of LSCO films occur. The diffusion voltages Vd and the fitting parameters E00 in the field emission/thermionic-field emission formula, as well as the in-plane resistivities of LSCO films have the similar temperature and magnetic field dependencies. It is believed that both of the superconductivities of LSCO films and the inhomogeneous Schottky interfaces between LSCO and SNTO are responsible for the I-V characteristics of the heterojunctions.
Simultaneously improved magnetization and polarization in BiFeO3 based multiferroic composites
Authors: Zhang Shuxia , Luo Wanju , Wang Lei , Wang Dongliang , Ma Yanwei
Published: March 2010

The multiferroic composites with nominal stoichiometry Bi0.8Dy0.2Fe1−yTiyO3+δ were fabricated by adding Ti to Bi0.8Dy0.2FeO3 through a two-stage solid-state reaction method. In the composites obtained, the major phase was isostructural to Bi0.8Dy0.2FeO3, and the secondary phase of Dy3Fe5O12 was also detected. Most interestingly, it was found that both the magnetization and electrical polarization were encouraged by the secondary phase Dy3Fe5O12. In addition to the improved ferroelectric property, a large saturation magnetization of 2.07 emu/g was reached for y≥0.03 samples. The simultaneously enhanced ferroelectric and magnetic properties achieved in the composites due to the existence of ferrimagnetic insulated Dy3Fe5O12 may have implications for further studies on BiFeO3 based materials.
A study on the carrier injection mechanism of the bottom-contact pentacene thin film transistor
Authors: Jung Keum-Dong , Kim Yoo Chul , Shin Hyungcheol , Park Byung-Gook , Lee Jong Duk , Cho Eou Sik , Kwon Sang Jik
Published: March 2010

For an analysis of the mechanism of carrier injection in the structure of bottom contact organic thin-film transistor (OTFT), Al blocking layer was applied to the source/drain electrode in variety of ways in the fabrication of bottom contact OTFT. From the comparison of the transfer characteristics of the OTFTs with different electrodes, it is obvious that the main direction of carrier injection is mainly dependent on the thickness of electrode. When the electrodes become thicker and thicker, the main carrier injection path is expected to be located at the side of the electrodes as well as the top of the electrodes.
Design constraints and guidelines for CdS/CdTe nanopillar based photovoltaics
Authors: Kapadia Rehan , Fan Zhiyong , Javey Ali
Published: March 2010

The performance dependence of a CdS/CdTe nanopillar solar cell on various device and materials parameters is explored while examining its performance limits through detailed device modeling. The optimized cell enables efficiencies >∼20% with minimal short circuit current dependence on bulk minority carrier diffusion length, demonstrating the efficient collection of photogenerated carriers, therefore, lowering the materials quality and purity constraints. Given the large p-n junction interface area, the interface recombination velocity is shown to have detrimental effect on the device performance of nanopillar solar cells. In that regard, the CdS/CdTe material system is optimal due to its low interface recombination velocity.
Effect of chemically ordered regions on the acoustic behaviors in Pb(Mg1/3Nb2/3)O3 studied by Brillouin scattering
Authors: Ko Jae-Hyeon , Kim Tae Hyun , Kojima Seiji , Long Xifa , Bokov Alexei A. , Ye Zuo-Guang
Published: March 2010

The longitudinal acoustic phonon modes of Pb(Mg1/3Nb2/3)O3 (PMN) and La-doped PMN were investigated by using Brillouin spectroscopy and compared. The acoustic behaviors of La-doped PMN were very similar to those of pure PMN in spite of its much larger size of the chemically ordered regions induced by La-doping. The relaxation times of La-doped PMN in the ergodic relaxor phase were almost the same to those of PMN. This result shows that the temperature evolution of dynamic polar nanoregions and the related high-frequency dynamics of PMN-based crystals in the gigahertz range are not affected by the size of the B-site cation-ordered regions.
Competition between electronic and vibrational predissociation dynamics of the HeBr2 and NeBr2 van der Waals molecules
Authors: Taylor Molly A. , Pio Jordan M. , van der Veer Wytze E. , Janda Kenneth C.
Published: March 2010

Direct measurements of the lifetimes of HeB79r2 and NeB79r2 B-state vibrational levels 10≤ν′≤20 have been performed using time-resolved optical pump-probe spectroscopy. The values do not obey the energy gap law for direct vibrational predissociation. For both molecules, the dissociation rate for ν′=11 is much faster than for ν′=12, and the ν′=13 rate is also faster than is consistent with the energy gap law. We attribute this unexpected behavior to an electronic predissociation channel. Based on Franck–Condon factors between the Br2 B-state vibrational wave functions and the possible Br–Br product wave functions, we surmise that either the Br2 Π3g(1g) or (2g) state is responsible for the electronic predissociation. To our knowledge, this is the first time electronic predissociation and direct Δν=−1 vibrational predissociation have been observed to be in competition for a wide range of vibrational levels. As such, this problem deserves a detailed theoretical analysis.
Bidirectional electrowetting actuation with voltage polarity dependence
Authors: Crane Nathan B. , Volinsky Alex A. , Mishra Pradeep , Rajgadkar Ajay , Khodayari Mehdi
Published: March 2010

This work presents an electrowetting system in which the actuation direction depends on the polarity of the applied voltage. Since electrowetting response depends on the voltage squared, it is typically independent of voltage sign to first order. However, the introduction of an electrochemical diode into the equivalent electrical circuit permits polarity-dependent behavior. Electrochemical diodes were created by making holes in the dielectric. The aluminum electrodes passivate and prevent current flow in one direction, creating diodelike electrical behavior with high breakdown voltage. The resulting actuation forces were directly measured and are of comparable magnitude for both actuation directions.
Electronic structure and contact resistance at an open-end carbon nanotube and copper interface
Authors: Gao Feng , Qu Jianmin , Yao Matthew
Published: March 2010

We report a quantum mechanics study on the electronic structure and contact resistance at an open-end carbon nanotube and copper interface. The local density of states near the carbon nanotube (CNT)/Cu interface are computed using density functional theory (DFT), and the transmission coefficient is calculated using a nonequilibrium Green’s function method in conjunction with DFT. The current-voltage relation of the simulating cell is obtained by using the Landauer–Buttiker formula, from which the contact resistance can be determined. Our results indicate that the contact resistance of the Cu/CNT/Cu system is comparable to that of solder/Cu interface in electronic packaging.
Conformational free energies of methyl-α-L-iduronic and methyl-β-D-glucuronic acids in water
Authors: Babin Volodymyr , Sagui Celeste
Published: March 2010

We present a simulation protocol that allows for efficient sampling of the degrees of freedom of a solute in explicit solvent. The protocol involves using a nonequilibrium umbrella sampling method, in this case, the recently developed adaptively biased molecular dynamics method, to compute an approximate free energy for the slow modes of the solute in explicit solvent. This approximate free energy is then used to set up a Hamiltonian replica exchange scheme that samples both from biased and unbiased distributions. The final accurate free energy is recovered via the weighted histogram analysis technique applied to all the replicas, and equilibrium properties of the solute are computed from the unbiased trajectory. We illustrate the approach by applying it to the study of the puckering landscapes of the methyl glycosides of α-L-iduronic acid and its C5 epimer β-D-glucuronic acid in water. Big savings in computational resources are gained in comparison to the standard parallel tempering method.
Analysis of the power dependent tuning of a varactor-loaded metamaterial at microwave frequencies
Authors: Huang Da , Poutrina Ekaterina , Smith David R.
Published: March 2010

We present an analysis of the nonlinear, power-dependent resonance frequency shift for two metamaterial mediums consisting of arrays of varactor-loaded split ring resonators (VLSRRs). We confirm that, over a limited range of power, a VLSRR medium can be described by its second and third order nonlinear susceptibilities, making it a useful analog medium for the quantitative investigation of other nonlinear phenomena that might be achieved using inherently nonlinear materials integrated into metamaterials. Experimental measurements of the resonance frequency shift with power from fabricated VLSRR samples are found to be in excellent agreement with the analytical model.
Limitations to band gap tuning in nitride semiconductor alloys
Authors: Gorczyca I. , Suski T. , Christensen N. E. , Svane A.
Published: March 2010

Relations between the band gaps of nitride alloys and their lattice parameters are presented and limits to tuning of the fundamental gap in nitride semiconductors are set by combining a large number of experimental data with ab initio theoretical calculations. Large band gap bowings obtained theoretically for GaxAl1−xN, InxGa1−xN, and InxAl1−xN for uniform as well as clustered arrangements of the cation atoms are considered in the theoretical analysis. It is shown that indium plays a particular role in nitride alloys being responsible for most of the observed effects.
A deep-level transient spectroscopy study of silicon interface states using different silicon nitride surface passivation schemes
Authors: Gong Chun , Simoen Eddy , Posthuma Niels , Van Kerschaver Emmanuel , Poortmans Jef , Mertens Robert
Published: March 2010

Low frequency direct plasma-enhanced chemical vapor deposited Si–SiNx interface properties with and without NH3 plasma pretreatment, with and without rapid thermal annealing (RTA) have been investigated with deep-level transient spectroscopy (DLTS) on both n- and p-type monocrystalline silicon samples. It is shown that four different defect states are identified at the Si–SiNx interface. Energy-dependent electron and hole capture cross sections were also measured by small-pulse DLTS. Samples with plasma NH3 pretreatment and RTA show the lowest DLTS signals, which suggest the lowest overall interface states density. Moreover, SiNx with RTA passivates interface states more efficiently in n-type Si compared with p-type Si; also the deep-level parameters change in n-type Si but not in p-type Si. The combination of plasma NH3 pretreatment and RTA is suggested for application in the solar cell fabrication.
Metal ion-doped SnO2 ordered porous films and their strong gas sensing selectivity
Authors: Jia Lichao , Cai Weiping , Wang Hongqiang
Published: March 2010

Based on a sol-gel technique and the colloidal monolayer template, ion-doped SnO2 ordered porous films were fabricated, and the corresponding gas-sensing properties were studied. The sensitivity to the given test gases strongly depends on the doping species and doping amount. Importantly, when the doping amount is 1% M, the Cr+3 and Pd+2 doped porous films demonstrate a greatly enhanced sensitivity and strong selectivity to ethanol and ammonia, respectively. The improved sensing properties are attributed to the doping-induced surface modification of the films. Such ion-doped porous films are expected to bring new opportunities for application of future porous film-based gas sensors.
Giant flexoelectricity in bent-core nematic liquid crystal elastomers
Authors: Harden J. , Chambers M. , Verduzco R. , Luchette P. , Gleeson J. T. , Sprunt S. , Jákli A.
Published: March 2010

Recently ferroelectric ceramic and bent-core nematic liquid crystals have demonstrated flexoelectricity (coupling between curvature strains to electric polarization) up to 104 times larger than the previous standards. This may allow for usable electromechanical devices. However, ceramics are too rigid to withstand large bending and bent-core nematic fluids must be physically supported—their technological applicability is still limited. In this paper, we show that novel side-chain bent-core nematic elastomers not only produce giant flexoelectricity but are also robust and flexible enough for microscale parasitic power generation.
Enhanced charge collection via nanoporous morphology in polymer solar cells
Authors: Lee Hang Ken , Jeon Ji Hye , Wang Dong Hwan , Park O. Ok , Kim Jai-Kyung , Im Sang Hyuk , Park Jong Hyeok
Published: March 2010

We demonstrated a simple and nonlithographic method that enlarges the active layer/metal electrode contact area in polymer solar cells by adding the thermal initiator 2,2′-azobisisobutyronitrile (AIBN) as a nanohole generating agent. From diffused light spectra and x-ray diffraction measurements, it is found that device performance enhancement comes not from a change in the charge carrier generation or transportation characteristics but from increased charge carrier collection due to the reduced contact resistance and shortened pathway to the electrode caused by enlarged interface area.
Dynamic Monte Carlo simulation in mixtures
Authors: Rutkai Gábor , Kristóf Tamás
Published: March 2010

The dynamic Monte Carlo technique is a widely used simulation tool but the parameters of the calculation have to be tuned to reflect the same dynamics as the corresponding molecular dynamics simulation. As the direct calibration of the dynamic Monte Carlo with molecular dynamics is a laborious task, we propose a new method that allows the standard dynamic Monte Carlo to realize the correct time proportionality in many-component systems without the need of corresponding molecular dynamics calculation. The method has been tested in various systems and the dynamic Monte Carlo results obtained by the proposed method were found to be in good agreement with the results of the control molecular dynamics simulations.
Galaxy and Mass Assembly (GAMA): Optimal Tiling of Dense Surveys with a Multi-Object Spectrograph
Authors: Robotham A. , Driver S. P. , Norberg P. , Baldry I. K. , Bamford S. P. , Hopkins A. M. , Liske J. , Loveday J. , Peacock J. A. , Cameron E. , Croom S. M. , Doyle I. F. , Frenk C. S. , Hill D. T. , Jones D. H. , van Kampen E. , Kelvin L. S. , Kuijken K. , Nichol R. C. , Parkinson H. R. , Popescu C. C. , Prescott M. , Sharp R. G. , Sutherland W. J. , Thomas D. , Tuffs R. J.
Published: March 2010

A heuristic greedy algorithm is developed for efficiently tiling spatially dense redshift surveys. In its first application to the Galaxy and MassAssembly (GAMA) redshift survey we find it rapidly improves the spatial uniformity of our data, and naturally corrects for any spatial bias introduced by the 2dF multi-object spectrograph. We make conservative predictions for the final state of the GAMA redshift survey after our final allocation of time, and can be confident that even if worse than typical weather affects our observations, all of our main survey requirements will be met.
Corrigendum to: A catch-all leguminous tree: Erythrina velutina visited and pollinated by vertebrates at an oceanic island
Authors: Sazima Ivan , Sazima Cristina , Sazima Marlies
Published: March 2010

Species of the pantropical genus Erythrina (Fabaceae) are visited by perching and/or hovering birds in the mainland. At the oceanic island of Fernando de Noronha, north-eastern Brazil, we found that Erythrina velutina Willd. blooms during the dry season and the flowers are visited by a small vertebrate assemblage. Flowers last 2 days and their stigmas remain receptive, although only first-day flowers produce nectar. Nectar is dilute and produced copiously. All terrestrial native vertebrates (three of them endemics), the dove Zenaida auriculata noronha, the perching birds Vireo gracilirostris and Elaenia ridleyana, and the lizard Euprepis atlanticus are regular visitors and pollinators. The features of E. velutina conform to those of passerine-pollinated species within the genus. Its nectar is a resource sought by the vertebrates, which visit the inflorescences from dawn to sunset. Since none of the visitors depends on nectar as a major food source, the flowers are likely to serve a dual purpose, i.e. water balance and energy intake, similarly to the findings for some Erythrina species in Neotropic and Palaeotropic mainlands. However, E. velutina is the only species within the genus that is visited and pollinated by doves and lizards.
Savanna woody plant dynamics: the role of fire and herbivory, separately and synergistically
Authors: Midgley Jeremy J. , Lawes Michael J. , Chamaillé-Jammes Simon
Published: March 2010

Although the demography of woody plants in savannas has long been shown to be due to many factors, there still is no consensus as to the relative importance of the top-down processes of fire and herbivory, nor on how fire and herbivory affect plant demography. We review the recent literature and suggest that further progress depends on the following: (i) a demographic framework with clear terminology and which focuses on recruitment, transitions and mortality, (ii) an understanding of mechanisms of how fire actually damages plants and how plants survive and out-grow this damage, mainly through height, bark thickness or diameter growth, (iii) an understanding of how losses in biomass due to herbivory may affect plant demography and, (iv) a consideration of interactions between fire and herbivory. Our synthesis suggests (i) strong recruitment limitation as well as some evidence of transition limitation by both fire and herbivory, (ii) that in some cases herbivory alone, notably by elephants and impala, can be more significant than fire alone, on woody plant population size, (iii) that fire and herbivory together are a lethal combination for woody plants and, (iv) that differences in strategies and responses of savanna plants to fire and herbivory are poorly explored.
Ovule ontogeny of Relbunium species in the evolutionary context of Rubiaceae
Authors: De Toni Karen L. G. , Mariath Jorge E. A.
Published: March 2010

Carpel and ovule ontogeny, gynosporogenesis and gynogametogenesis in species of Relbunium were studied in order to provide additional data distinguishing evolutionary embryological characters. No significant differences in either ontogeny or morphology were observed among the species. The following characteristics are common to all species studied: (1) an independent development between the establishment of carpels and placenta meristem; (2) a bi-layered structure of the ovule primordia; and (3) a remnant gynosporium of the ovules, which contains the gynospores and binucleated gametophytes that migrate towards the micropyle where their development is concluded. The embryological characters are explored, and additional data are provided for the analyses of the evolutionary tendencies to Relbunium (Endl.) Benth. & Hook. f. species. In accordance with previous evolutionary proposals, the analysed species can be compared with the Galium type.
Karyotypic diversification and its contribution to the taxonomy of Eleocharis (Cyperaceae) from Brazil
Authors: Maximiano da Silva Carlos Roberto , Trevisan Rafael , González-Elizondo Maria Socorro , Ferreira Josué Maldonado , Vanzela André Luís Laforga
Published: March 2010

A karyotype analysis of 147 populations of 25 Brazilian species of Eleocharis (Cyperaceae) was carried out, including representatives of the three subgenera that occur in the country: Limnochloa, Scirpidium and Eleocharis. The analyses showed chromosomes without centromeres, but with terminal nucleolar constrictions (satellites) in some chromosomes. The chromosome numbers varied from 2n = 6 in E. subarticulata and E. maculosa to 2n = 60 in E. laeviglumis, but the chromosome basic number x = 5 was confirmed. Species of the subgenera Eleocharis and Scirpidium possess fewer and larger chromosomes, while those in the subgenus Limnochloa have small and more numerous chromosomes. These features indicate that the karyotypes of the subgenera Eleocharis and Scirpidium are more closely related, in agreement with morphological and phylogenetical data. The representatives of the section Eleocharis exhibited the largest differences in chromosome number and size, probably due to chromosome fission and fusion. Polyploidy was the most common event in this group. Nevertheless, most of the studied species exhibited regular meiosis with only bivalent formation, even the polyploids, such as in E. geniculata and E. sellowiana. The cytogenetic information obtained showed quite variable karyotypes with chromosomes gradually decreasing in size, and predominance of polyploidy. These results are useful in the differentiation of the subgenera.
Cytological analysis of hybrid embryos of intergeneric crosses between Salix viminalis and Populus species
Authors: Bagniewska-Zadworna Agnieszka , Wojciechowicz Maria K. , Zenkteler Maciej , Jeżowski Stanisław , Zenkteler Elżbieta
Published: March 2010

Intergeneric hybridisation between Salix viminalis L. as the female and four Populus species (Populus trichocarpa, P. tremula, P. × canadensis and P. simonii) as male pollen donors was performed by in vitro stigma pollination. To overcome postzygotic barriers, transfer of hybrid embryos to new medium is necessary. We carried out detailed ultrastructural analyses to establish: (i) at which stage of embryo development the first signs of programmed cell death (PCD) could be detected; and (ii) at which stage the lack of serious or irreversible changes guaranteed that advanced development of hybrid plants could occur after embryo rescue. Transmission electron microscopy and confocal laser scanning microscopy revealed the presence of both developing and degenerating embryos. Developing globular, heart-shaped, and early cotyledonary embryos contained cells of correct ultrastructure. The only sign of intergeneric hybridisation was a delay in development for a few days, in comparison with control embryos. The earliest indicators of embryo degeneration were noted at 9 days after pollination (DAP). The most common indicators were excessive embryo vacuolisation, which was characterised by a large number of vesicles and formation of small vacuoles, as well as enlarged central vacuoles. Extended plastid thylakoids, folding of the cell wall, and autophagosomes were observed. Our detailed investigation of PCD in hybrid embryos enabled us to conclude that the embryo rescue technique was most effective in intergeneric willow × poplar crosses if applied between 9 and 16 DAP.
Distinct frontal systems for response inhibition, attentional capture, and error processing
Authors: Sharp D. J. , Bonnelle V. , De Boissezon X. , Beckmann C. F. , James S. G. , Patel M. C. , Mehta M. A.
Published: March 2010

Stopping an action in response to an unexpected event requires both that the event is attended to, and that the action is inhibited. Previous neuroimaging investigations of stopping have failed to adequately separate these cognitive elements. Here we used a version of the widely used Stop Signal Task that controls for the attentional capture of stop signals. This allowed us to fractionate the contributions of frontal regions, including the right inferior frontal gyrus and medial frontal cortex, to attentional capture, response inhibition, and error processing. A ventral attentional system, including the right inferior frontal gyrus, has been shown to respond to unexpected stimuli. In line with this evidence, we reasoned that lateral frontal regions support attentional capture, whereas medial frontal regions, including the presupplementary motor area (pre-SMA), actually inhibit the ongoing action. We tested this hypothesis by contrasting the brain networks associated with the presentation of unexpected stimuli against those associated with outright stopping. Functional MRI images were obtained in 26 healthy volunteers. Successful stopping was associated with activation of the right inferior frontal gyrus, as well as the pre-SMA. However, only activation of the pre-SMA differentiated stopping from a high-level baseline that controlled for attentional capture. As expected, unsuccessful attempts at stopping activated the anterior cingulate cortex. In keeping with work in nonhuman primates these findings demonstrate that successful motor inhibition is specifically associated with pre-SMA activation.
Nuclear entry of a cGMP-dependent kinase converts transient into long-lasting olfactory adaptation
Authors: Lee Jin I. , O'Halloran Damien M. , Eastham-Anderson Jeffery , Juang Bi-Tzen , Kaye Julia A. , Scott Hamilton O. , Lesch Bluma , Goga Andrei , L'Etoile Noelle D.
Published: March 2010

To navigate a complex and changing environment, an animal's sensory neurons must continually adapt to persistent cues while remaining responsive to novel stimuli. Long-term exposure to an inherently attractive odor causes
Caenorhabditis elegans
to ignore that odor, a process termed odor adaptation. Odor adaptation is likely to begin within the sensory neuron, because it requires factors that act within these cells at the time of odor exposure. The process by which an olfactory sensory neuron makes a decisive shift over time from a receptive state to a lasting unresponsive one remains obscure. In
C. elegans,
adaptation to odors sensed by the AWC pair of olfactory neurons requires the cGMP-dependent protein kinase EGL-4. Using a fully functional, GFP-tagged EGL-4, we show here that prolonged odor exposure sends EGL-4 into the nucleus of the stimulated AWC neuron. This odor-induced nuclear translocation correlates temporally with the stable dampening of chemotaxis that is indicative of long-term adaptation. Long-term adaptation requires cGMP binding residues as well as an active EGL-4 kinase. We show here that EGL-4 nuclear accumulation is both necessary and sufficient to induce long-lasting odor adaptation. After it is in the AWC nucleus, EGL-4 decreases the animal's responsiveness to AWC-sensed odors by acting downstream of the primary sensory transduction. Thus, the EGL-4 protein kinase acts as a sensor that integrates odor signaling over time, and its nuclear translocation is an instructive switch that allows the animal to ignore persistent odors.
A conserved tetraspanin subfamily promotes Notch signaling in
Caenorhabditis elegans
and in human cells
Authors: Dunn Cory D. , Sulis Maria Luisa , Ferrando Adolfo A. , Greenwald Iva
Published: March 2010

The cytosolic domain of Notch is a membrane-tethered transcription factor. Ligand binding ultimately leads to γ-secretase cleavage within the transmembrane domain, allowing the intracellular domain to translocate to the nucleus and activate target gene transcription. Constitutive Notch signaling has been associated with human cancers such as T cell acute lymphoblastic leukemia (T-ALL). As tetraspanins have been implicated in many different signaling processes, we assessed their potential contribution to Notch signaling. We used a genetic assay in
Caenorhabditis elegans
to identify TSP-12 as a positive factor for Notch activity in several cellular contexts. Then, using a cell culture system, we showed that two human TSP-12 orthologs, TSPAN33 and TSPAN5, promote Notch activity and are likely to act at the γ-secretase cleavage step. We also acquired evidence for functional redundancy among tetraspanins in both
C. elegans
and human cells. Selective inhibition of tetraspanins may constitute an anti-NOTCH therapeutic approach to reduce γ-secretase activity.
Influence of prime lexicality, frequency, and pronounceability on the masked onset priming effect
Authors: Dimitropoulou Maria , Duñabeitia Jon Andoni , Carreiras Manuel
Published: March 2010

The present study investigates the origins of the masked onset priming effect (MOPE). There are two alternative interpretations that account for most of the evidence reported on the MOPE, so far. The speech planning account (SP) identifies the locus of the MOPE in the preparation of the speech response. In contrast, the dual-route theory proposes that the effect arises as a result of the processing of the prime by the nonlexical route. In a series of masked onset priming word naming experiments we test the validity of these accounts by manipulating the primes’ frequency, their lexical status, and pronounceability. We found consistent MOPEs of similar magnitude with high- and low-frequency prime words as well as with pronounceable nonwords. Contrarily, when primes consisted of unpronounceable consonantal strings the effect disappeared, suggesting that pronounceability of the prime is a prerequisite for the emergence of the MOPE. These results are in accordance with the predictions of the SP account. The pattern of effects obtained in the present study further defines the origins of the MOPE.
The synthesis of superhydrophobic Bi2S3complex nanostructures
Authors: Xiao Yujiang , Cao Huaqiang , Liu Kaiyu , Zhang Sichun , Chernow Victoria
Published: March 2010

In this paper, we report a biomolecule-assisted soft chemistry route for constructing complex Bi2S3nanostructures that exhibit controlled wetting behavior. The as-synthesized sample was characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), field emission SEM (FE-SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), Fourier transform infrared (FT-IR), Raman, x-ray photoelectron (XPS) and photoluminescence (PL). The Raman spectra indicate that the surface optical (SO) phonon mode occurs in Bi2S3nanoparticles. The SO phonon mode is attributed to the defects on the surface of Bi2S3nanoparticles. In addition, the possible formation mechanism of the self-assembled urchin-like Bi2S3complex nanostructures is discussed. The established complex nanostructure can control the surface topology of a membrane to create a superhydrophobic surface. A water contact angle (CA) of > 150° of the as-synthesized Bi2S3complex nanostructures can be obtained, which may find potential application in environmental chemistry.
Yeast Mpk1 Cell Wall Integrity Mitogen-activated Protein Kinase Regulates Nucleocytoplasmic Shuttling of the Swi6 Transcriptional Regulator
Authors: Kim Ki-Young , Truman Andrew W. , Caesar Stefanie , Schlenstedt Gabriel , Levin David E.
Published: March 2010

The yeast SBF transcription factor is a heterodimer comprised of Swi4 and Swi6 that has a well defined role in cell cycle-specific transcription. SBF serves a second function in the transcriptional response to cell wall stress in which activated Mpk1 mitogen-activated protein kinase of the cell wall integrity signaling pathway forms a complex with Swi4, the DNA binding subunit of SBF, conferring upon Swi4 the ability to bind DNA and activate transcription of FKS2. Although Mpk1–Swi4 complex formation and transcriptional activation of FKS2 does not require Mpk1 catalytic activity, Swi6 is phosphorylated by Mpk1 and must be present in the Mpk1-Swi4 complex for transcriptional activation of FKS2. Here, we find that Mpk1 regulates Swi6 nucleocytoplasmic shuttling in a biphasic manner. First, formation of the Mpk1-Swi4 complex recruits Swi6 to the nucleus for transcriptional activation. Second, Mpk1 negatively regulates Swi6 by phosphorylation on Ser238, which inhibits nuclear entry. Ser238 neighbors a nuclear localization signal (NLS) whose function is blocked by phosphorylation at Ser238 in a manner similar to the regulation by Cdc28 of another Swi6 NLS, revealing a mechanism for the integration of multiple signals to a single endpoint. Finally, the Kap120 β-importin binds the Mpk1-regulated Swi6 NLS but not the Cdc28-regulated NLS.
Analyzing the Birth and Propagation of Two Distinct Prions, [PSI+] and [Het-s]y, in Yeast
Authors: Mathur Vidhu , Taneja Vibha , Sun Yidi , Liebman Susan W.
Published: March 2010

Various proteins, like the infectious yeast prions and the noninfectious human Huntingtin protein (with expanded polyQ), depend on a Gln or Asn (QN)-rich region for amyloid formation. Other prions, e.g., mammalian PrP and the [Het-s] prion of Podospora anserina, although still able to form infectious amyloid aggregates, do not have QN-rich regions. Furthermore, [Het-s] and yeast prions appear to differ dramatically in their amyloid conformation. Despite these differences, a fusion of the Het-s prion domain to GFP (Het-sPrD-GFP) can propagate in yeast as a prion called [Het-s]y. We analyzed the properties of two divergent prions in yeast: [Het-s]yand the native yeast prion [PSI+] (prion form of translational termination factor Sup35). Curiously, the induced appearance and transmission of [PSI+] and [Het-s]yaggregates is remarkably similar. Overexpression of tagged prion protein (Sup35-GFP or Het-sPrD-GFP) in nonprion cells gives rise to peripheral, and later internal, ring/mesh-like aggregates. The cells with these ring-like aggregates give rise to daughters with one (perivacuolar) or two (perivacuolar and juxtanuclear) dot-like aggregates per cell. These line, ring, mesh, and dot aggregates are not really the transmissible prion species and should only be regarded as phenotypic markers of the presence of the prions. Both [PSI+] and [Het-s]yfirst appear in daughters as numerous tiny dot-like aggregates, and both require the endocytic protein, Sla2, for ring formation, but not propagation.
Stepwise Assembly of Dimeric F1Fo-ATP Synthase in Mitochondria Involves the Small Fo-Subunits k and i
Authors: Wagner Karina , Perschil Inge , Fichter Christiane D. , van der Laan Martin
Published: March 2010

F1Fo-ATP synthase is a key enzyme of oxidative phosphorylation that is localized in the inner membrane of mitochondria. It uses the energy stored in the proton gradient across the inner mitochondrial membrane to catalyze the synthesis of ATP from ADP and phosphate. Dimeric and higher oligomeric forms of ATP synthase have been observed in mitochondria from various organisms. Oligomerization of ATP synthase is critical for the morphology of the inner mitochondrial membrane because it supports the generation of tubular cristae membrane domains. Association of individual F1Fo-ATP synthase complexes is mediated by the membrane-embedded Fo-part. Several subunits were mapped to monomer-monomer-interfaces of yeast ATP synthase complexes, but only Su e (Atp21) and Su g (Atp20) have so far been identified as crucial for the formation of stable dimers. We show that two other small Fo-components, Su k (Atp19) and Su i (Atp18) are involved in the stepwise assembly of F1Fo-ATP synthase dimers and oligomers. We have identified an intermediate form of the ATP synthase dimer, which accumulates in the absence of Su i. Moreover, our data indicate that Su i facilitates the incorporation of newly synthesized subunits into ATP synthase complexes.