bluuebunny/crossref_metadata_2025 huggingface dataset:
Resistance and resilience of the forest soil microbiome to logging-associated compaction
Authors: Hartmann Martin , Niklaus Pascal A , Zimmermann Stephan , Schmutz Stefan , Kremer Johann , Abarenkov Kessy , Lüscher Peter , Widmer Franco , Frey Beat
Published: September 2013

Soil compaction is a major disturbance associated with logging, but we lack a fundamental understanding of how this affects the soil microbiome. We assessed the structural resistance and resilience of the microbiome using a high-throughput pyrosequencing approach in differently compacted soils at two forest sites and correlated these findings with changes in soil physical properties and functions. Alterations in soil porosity after compaction strongly limited the air and water conductivity. Compaction significantly reduced abundance, increased diversity, and persistently altered the structure of the microbiota. Fungi were less resistant and resilient than bacteria; clayey soils were less resistant and resilient than sandy soils. The strongest effects were observed in soils with unfavorable moisture conditions, where air and water conductivities dropped well below 10% of their initial value. Maximum impact was observed around 6–12 months after compaction, and microbial communities showed resilience in lightly but not in severely compacted soils 4 years post disturbance. Bacteria capable of anaerobic respiration, including sulfate, sulfur, and metal reducers of the Proteobacteria and Firmicutes, were significantly associated with compacted soils. Compaction detrimentally affected ectomycorrhizal species, whereas saprobic and parasitic fungi proportionally increased in compacted soils. Structural shifts in the microbiota were accompanied by significant changes in soil processes, resulting in reduced carbon dioxide, and increased methane and nitrous oxide emissions from compacted soils. This study demonstrates that physical soil disturbance during logging induces profound and long-lasting changes in the soil microbiome and associated soil functions, raising awareness regarding sustainable management of economically driven logging operations.
Metagenomic analysis of size-fractionated picoplankton in a marine oxygen minimum zone
Authors: Ganesh Sangita , Parris Darren J , DeLong Edward F , Stewart Frank J
Published: September 2013

Marine oxygen minimum zones (OMZs) support diverse microbial communities with roles in major elemental cycles. It is unclear how the taxonomic composition and metabolism of OMZ microorganisms vary between particle-associated and free-living size fractions. We used amplicon (16S rRNA gene) and shotgun metagenome sequencing to compare microbial communities from large (>1.6 μm) and small (0.2–1.6 μm) filter size fractions along a depth gradient in the OMZ off Chile. Despite steep vertical redox gradients, size fraction was a significantly stronger predictor of community composition compared to depth. Phylogenetic diversity showed contrasting patterns, decreasing towards the anoxic OMZ core in the small size fraction, but exhibiting maximal values at these depths within the larger size fraction. Fraction-specific distributions were evident for key OMZ taxa, including anammox planctomycetes, whose coding sequences were enriched up to threefold in the 0.2–1.6 μm community. Functional gene composition also differed between fractions, with the >1.6 μm community significantly enriched in genes mediating social interactions, including motility, adhesion, cell-to-cell transfer, antibiotic resistance and mobile element activity. Prokaryotic transposase genes were three to six fold more abundant in this fraction, comprising up to 2% of protein-coding sequences, suggesting that particle surfaces may act as hotbeds for transposition-based genome changes in marine microbes. Genes for nitric and nitrous oxide reduction were also more abundant (three to seven fold) in the larger size fraction, suggesting microniche partitioning of key denitrification steps. These results highlight an important role for surface attachment in shaping community metabolic potential and genome content in OMZ microorganisms.
Does dopamine block the spawning of the acroporid coral Acropora tenuis?
Authors: Isomura N. , Yamauchi C. , Takeuchi Y. , Takemura A.
Published: September 2013

Most corals undergo spawning after a particular moon phase, but how moon-related spawning is endogenously regulated in corals remains unknown. The objective of the present study was to evaluate whether dopamine (DA) affects spawning in Acropora tenuis. When pieces of four A. tenuis colonies were reared under a natural photoperiod and water temperature, spawning was observed after the predicted moon phase. After exposure to water containing DA at 0.1 μM, pieces of the same colonies only released 5 to 10 bundles. Co-treatment with DA and pimozide (D1 and D2 receptors antagonist), but not domperidone (D2 receptor antagonist), induced mass release of bundles from the colonies. A cross-experiment revealed high fertilization rates between the control colonies (95%) and between the control and DA-treated colonies (90%), suggesting that gametes developed normally in coral tissue. Therefore, DA appears to have an inhibitory effect on the spawning of A. tenuis.
Endoplasmic reticulum-associated ubiquitin-conjugating enzyme Ube2j1 is a novel substrate of MK2 (MAPKAP kinase-2) involved in MK2-mediated TNFα production
Authors: Menon Manoj B. , Tiedje Christopher , Lafera Juri , Ronkina Natalia , Konen Timo , Kotlyarov Alexey , Gaestel Matthias
Published: September 2013

The p38 MAPK (mitogen-activated protein kinase)/MK2 [MAPKAP (MAPK-activated protein) kinase-2] signalling pathway is a major regulator of stress- and cytokine-induced gene expression at the transcriptional and post-transcriptional level. Using phosphoproteomics we identified the ER (endoplasmic reticulum)-associated ubiquitin-conjugating enzyme Ube2j1 as a potential substrate of MK2. We demonstrate that Ube2j1 is phosphorylated in a cytokine-, cytosolic stress- and LPS (lipopolysaccharide)-induced manner. The cytosolic stress-induced phosphorylation of Ube2j1 proceeds at Ser184, a site described previously to be phosphorylated in response to ER stress, which is located in a perfect MK2 consensus motif. The cytosolic stress-induced phosphorylation of Ube2j1, but not its ER-stress-induced phosphorylation is sensitive to p38/MK2 inhibitors and abrogated in MK2/MK3-deficient cells. In a pull-down assay we demonstrate the interaction of MK2 with Ube2j1 in HEK (human embryonic kidney)-293T cells. Furthermore, MK2 is able to phosphorylate recombinant Ube2j1, but not the S184A mutant in an in vitro kinase assay. These findings strongly suggest that MK2 directly phosphorylates Ube2j1 at Ser184 upon p38-activating stress in vivo. However, ectopically expressed Ube2j1-S184A mutant displays ubiquitinating activity towards the model substrate ER-synthesized T-cell receptor-α similar to that of the wild-type protein. Interestingly, Ube2j1 is phosphorylated in response to LPS also in macrophages and contributes to MK2-dependent TNFα biosynthesis by a so far unknown mechanism.
Graphene as discharge layer for electron beam lithography on insulating substrate
Authors: Liu Junku , Li Qunqing , Ren Mengxin , Zhang Lihui , Chen Mo , Fan Shoushan
Published: September 2013

Charging of insulating substrates is a common problem during Electron Beam lithography (EBL), which deflects the beam and distorts the pattern. A homogeneous, electrically conductive, and transparent graphene layer is used as a discharge layer for EBL processes on insulating substrates. The EBL resolution is improved compared with the metal discharge layer. Dense arrays of holes with diameters of 50 nm and gratings with line/space of 50/30 nm are obtained on quartz substrate. The pattern placement errors and proximity effect are suppressed over a large area and high quality complex nanostructures are fabricated using graphene as a conductive layer.
Nonequilibrium Ornstein-Zernike relation for Brownian many-body dynamics
Authors: Brader Joseph M. , Schmidt Matthias
Published: September 2013

We derive a dynamic Ornstein-Zernike equation for classical fluids undergoing overdamped Brownian motion and driven out of equilibrium. Inhomogeneous two-time correlation functions are obtained from functional differentiation of the one-body density and current with respect to an appropriately chosen external field. Functional calculus leads naturally to non-Markovian equations of motion for the two-time correlators. Memory functions are identified as functional derivatives of a space- and time-nonlocal power dissipation functional. We propose an excess (over ideal gas) dissipation functional that both generates mode-coupling theory for the two-body correlations and extends dynamical density functional theory for the one-body fields, thus unifying the two approaches.
Long-range interactions and the sign of natural amplitudes in two-electron systems
Authors: Giesbertz Klaas J. H. , van Leeuwen Robert
Published: September 2013

In singlet two-electron systems, the natural occupation numbers of the one-particle reduced density matrix are given as squares of the natural amplitudes which are defined as the expansion coefficients of the two-electron wave function in a natural orbital basis. In this work, we relate the sign of the natural amplitudes to the nature of the two-body interaction. We show that long-range Coulomb-type interactions are responsible for the appearance of positive amplitudes and give both analytical and numerical examples that illustrate how the long-distance structure of the wave function affects these amplitudes. We further demonstrate that the amplitudes show an avoided crossing behavior as function of a parameter in the Hamiltonian and use this feature to show that these amplitudes never become zero, except for special interactions in which infinitely many of them can become zero simultaneously when changing the interaction strength. This mechanism of avoided crossings provides an alternative argument for the non-vanishing of the natural occupation numbers in Coulomb systems.
Phase diagram of compressively strained nickelate thin films
Authors: Disa A. S. , Kumah D. P. , Ngai J. H. , Specht E. D. , Arena D. A. , Walker F. J. , Ahn C. H.
Published: September 2013

The complex phase diagrams of strongly correlated oxides arise from the coupling between physical and electronic structure. This can lead to a renormalization of the phase boundaries when considering thin films rather than bulk crystals due to reduced dimensionality and epitaxial strain. The well-established bulk RNiO3 phase diagram shows a systematic dependence between the metal-insulator transition and the perovskite A-site rare-earth ion, R. Here, we explore the equivalent phase diagram for nickelate thin films under compressive epitaxial strain. We determine the metal-insulator phase diagram for the solid solution of Nd1-yLayNiO3 thin films within the range 0 ≤ y ≤ 1. We find qualitative similarity between the films and their bulk analogs, but with an overall renormalization in the metal-insulator transition to lower temperature. A combination of x-ray diffraction measurements and soft x-ray absorption spectroscopy indicates that the renormalization is due to increased Ni–O bond hybridization for coherently strained thin films.
From nanotubes to single crystals: Co doped TiO2
Authors: Jaćimović J. , Horváth E. , Náfrádi B. , Gaál R. , Nikseresht N. , Berger H. , Forró L. , Magrez A.
Published: September 2013

Millimeter-sized cobalt doped rutile crystals with a bi-pyramidal shape are obtained by chemical vapour transport using scroll-type H2Ti3O7 nanotubes as a precursor in which Co2+ ions are introduced by a simple ion exchange method prior to the growth. Despite the low concentration of Co2+ dopants (5 × 1019 cm−3), the resistivity of the single crystal shows a metallic behaviour above 50 K and the Seebeck coefficient has the signatures of polaronic quasiparticles. The magnetic properties of the material show a weak anti-ferromagnetic interaction between the spins on Co atoms below 50 K. This synthesis method could be beneficial for the growth of a large variety of doped TiO2 single crystals.
Demixing transition, structure, and depletion forces in binary mixtures of hard-spheres: The role of bridge functions
Authors: López-Sánchez Erik , Estrada-Álvarez César D. , Pérez-Ángel Gabriel , Méndez-Alcaraz José Miguel , González-Mozuelos Pedro , Castañeda-Priego Ramón
Published: September 2013

Asymmetric binary mixtures of hard-spheres exhibit several interesting thermodynamic phenomena, such as multiple kinds of glassy states. When the degrees of freedom of the small spheres are integrated out from the description, their effects are incorporated into an effective pair interaction between large spheres known as the depletion potential. The latter has been widely used to study both the phase behavior and dynamic arrest of the big particles. Depletion forces can be accounted for by a contraction of the description in the multicomponent Ornstein-Zernike equation [R. Castañeda-Priego, A. Rodríguez-López, and J. M. Méndez-Alcaraz, Phys. Rev. E 73, 051404 (2006)]10.1103/PhysRevE.73.051404. Within this theoretical scheme, an approximation for the difference between the effective and bare bridge functions is needed. In the limit of infinite dilution, this difference is irrelevant and the typical Asakura-Osawa depletion potential is recovered. At higher particle concentrations, however, this difference becomes important, especially where the shell of first neighbors is formed, and, as shown here, cannot be simply neglected. In this work, we use a variant of the Verlet expression for the bridge functions to highlight their importance in the calculation of the depletion potential at high densities and close to the spinodal decomposition. We demonstrate that the modified Verlet closure predicts demixing in binary mixtures of hard spheres for different size ratios and compare its predictions with both liquid state and density functional theories, computer simulations, and experiments. We also show that it provides accurate correlation functions even near the thermodynamic instability; this is explicitly corroborated with results of molecular dynamics simulations of the whole mixture. Particularly, our findings point toward a possible universal behavior of the depletion potential around the spinodal line.
Size of a crystal nucleus in the isothermal crystallization of supercooled liquid
Authors: Lee Heon Sang
Published: September 2013

We present an alternative to classical nucleation theory (CNT). We introduce a size-dependent surface energy into the total Gibbs free-energy of formation of a crystal (ΔG). We consider the free-energy in the core part of the total volume of crystal and the free-energy in the surface-layer part of it, separately, for the evaluation of ΔG. As a result, we present an explicit model to evaluate a characteristic size of an initial nucleus that differs from the critical nucleus of CNT, but whose temperature dependence agrees well with that reported for the temperature dependency initial fold length of isotactic polystyrene and polyethylene in the literature. Our model has fitted the experimental data in the literature with only one adjustable parameter that is defined as nucleation constant. The nucleation constant is the Gibbs free-energy difference between the crystal and supercooled liquid phases for the volume of initial nucleus. We also present an expression to approximate the evolution of free-energy in the surface-layer part of crystal during the crystal growth.
Investigation on streamers propagating into a helium jet in air at atmospheric pressure: Electrical and optical emission analysis
Authors: Gazeli K. , Svarnas P. , Vafeas P. , Papadopoulos P. K. , Gkelios A. , Clément F.
Published: September 2013

The plasma produced due to streamers guided by a dielectric tube and a helium jet in atmospheric air is herein studied electrically and optically. Helium streamers are produced inside the dielectric tube of a coaxial dielectric-barrier discharge and, upon exiting the tube, they propagate into the helium jet in air. The axisymmetric velocity field of the neutral helium gas while it penetrates the air is approximated with the PISO algorithm. At the present working conditions, turbulence helium flow is avoided. The system is driven by sinusoidal high voltage of variable amplitude (0–11 kV peak-to-peak) and frequency (5–20 kHz). It is clearly shown that a prerequisite for streamer development is a continuous flow of helium, independently of the sustainment or not of the dielectric-barrier discharge. A parametric study is carried out by scanning the range of the operating parameters of the system and the optimal operational window for the longest propagation path of the streamers in air is determined. For this optimum, the streamer current impulses and the spatiotemporal progress of the streamer UV-visible emission are recorded. The streamer mean propagation velocity is as well measured. The formation of copious reactive emissive species is then considered (in terms of intensity and rotational temperatures), and their evolution along the streamer propagation path is mapped. The main claims of the present work contribute to the better understanding of the physicochemical features of similar systems that are currently applied to various interdisciplinary engineering fields, including biomedicine and material processing.
Compositional engineering of BaTiO3/(Ba,Sr)TiO3 ferroelectric superlattices
Authors: Ortega N. , Kumar Ashok , Resto Oscar , Maslova O. A. , Yuzyuk Yu. I. , Scott J. F. , Katiyar Ram S.
Published: September 2013

Epitaxial strain is one of the major factors influencing physical properties of artificial superlattice (SL) structures. One way to control the local stress in epitaxial films is altering the lattice parameters by doping. Superlattices of BT/Ba(1−x)SrxTiO3 (BT/BST) with x = (0, 0.3, 0.4, 0.5, 0.6, 0.7, 1) with a modulation period of about 80–90 Å were grown on La0.67Sr0.33MnO3 coated (100) MgO substrates by pulsed laser deposition technique. The modulated structure of the thin films was confirmed by x-ray diffraction, Raman spectroscopy, and transmission electron microscopy. The increase in Sr concentration in BST layers of the SLs results in an increase in in-plane (a) and out-plane (c) compressive/tensile misfit strains in the BT/BST layers, respectively. The highest value of the dielectric constant was obtained for BT/Ba0.3Sr0.7TiO3 (BT/BST3070) and BT/Ba0.7Sr0.3TiO3 (BT/BST7030) SLs. Slim, asymmetric, but well-saturated ferroelectric hysteresis loops were observed in all SLs. Additionally, BT/BST SLs exhibited exceptionally high electric field stress sustainability over a wide range of frequency (10 kHz) and temperature (80–350 K). Temperature-dependent dielectric and ferroelectric properties show a ferroelectric relaxor behavior when the Sr content is increased in the BST layer of the SLs. Analysis of polarization versus temperature data using Landau-Devonshire theory suggests a second-order ferroelectric phase transition in these SLs. This structure can therefore be attractive in the design of a new kind of dielectric device capable in both high power and high energy density applications.
Higher-order discrete variational problems with constraints
Authors: Colombo Leonardo , Martín de Diego David , Zuccalli Marcela
Published: September 2013

An interesting family of geometric integrators for Lagrangian systems can be defined using discretizations of the Hamilton's principle of critical action. This family of geometric integrators is called variational integrators. In this paper, we derive new variational integrators for higher-order Lagrangian mechanical system subjected to higher-order constraints. From the discretization of the variational principles, we show that our methods are automatically symplectic and, in consequence, with a very good energy behavior. Additionally, the symmetries of the discrete Lagrangian imply that momentum is conserved by the integrator. Moreover, we extend our construction to variational integrators where the Lagrangian is explicitly time-dependent. Finally, some motivating applications of higher-order problems are considered; in particular, optimal control problems for explicitly time-dependent underactuated systems and an interpolation problem on Riemannian manifolds.
Evidence of nanostructuration from the heat capacities of the 1,3-dialkylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid series
Authors: Rocha Marisa A. A. , Coutinho João A. P. , Santos Luís M. N. B. F.
Published: September 2013

In the present work, the heat capacities at T = 298.15 K of 1,3-dialkylimidazolium bis(trifluoromethylsulfonyl)imide, [CN/2CN/2im][NTf2], were measured, for the first time, using a high-precision heat capacity drop calorimeter, with an uncertainty of less than 0.15%. Based on the obtained results, it was possible to evaluate the effect of the cation symmetry on the heat capacity data through a comparative analysis with the [CN-1C1im][NTf2] ionic liquid series. The molar heat capacities of the [CN/2CN/2im][NTf2] ionic liquids series present a less pronounced deviation from the linearity along the alkyl chain length than the asymmetric based ionic liquids series. Lower molar heat capacities for the symmetric than the asymmetric series were observed, being this difference more evident for the specific and volumic heat capacities. As observed for the [CN−1C1im][NTf2] series, a trend shift in the heat capacities at [C6C6im][NTf2] was found that reflects the impact of nonpolar region nanostructuration on the thermophysical properties of the ionic liquids. The profile of the two regions is in agreement with the expected effect arising from the nanostructuration in ionic liquids. The results obtained in the present work show a clear indication that for the symmetric series, [CN/2CN/2im][NTf2], the starting of the liquid phase nanostructuration/alkyl chain segregation occurs around [C6C6im][NTf2].
Note: Arbitrary periodical mechanical vibrations can be realized in the resonant state based on multiple tuning fork structure
Authors: He Liangguo , Pan Chengliang , Wang Hongbo , Feng Zhihua
Published: September 2013

We develop a novel approach to match harmonics and vibration modes based on the mechanism of multiple tuning fork structure (MTFS), through which it is promising to realize arbitrary periodical vibrations in the resonant state. A prototype three-layer MTFS with first three harmonics is presented to verify the feasibility of the proposed principle. The matching process and experimental results confirm the unique advantages of MTFS, as discussed in the theoretical analysis. Typical periodical motions, including sawtooth, square, half-wave rectified, and full-wave rectified waveforms, are achieved by the syntheses of resonant harmonics.
Fe-based nanoparticles as tunable magnetic particle hyperthermia agents
Authors: Simeonidis K. , Martinez-Boubeta C. , Balcells Ll. , Monty C. , Stavropoulos G. , Mitrakas M. , Matsakidou A. , Vourlias G. , Angelakeris M.
Published: September 2013

Magnetic hyperthermia, an alternative anticancer modality, is influenced by the composition, size, magnetic properties, and degree of aggregation of the corresponding nanoparticle heating agents. Here, we attempt to evaluate the AC magnetic field heating response of Fe-based nanoparticles prepared by solar physical vapor deposition, a facile, high-yield methodology. Nanoparticle systems were grown by evaporating targets of Fe and Fe3O4 with different stoichiometry. It is observed that Fe3O4 nanoparticles residing in the magnetic monodomain region exhibit increased heating efficiency together with high specific loss power values above 0.9 kW/g at 765 kHz and 24 kA/m, compared with that of 0.1 kW/g for zero-valent Fe nanoparticles under the same conditions. The enhanced performance of Fe3O4 nanoparticles under the range of field explored (12–24 kA/m) may be attributed to the activation of a magnetic hysteresis loss mechanism when the applied AC field surpasses the particle anisotropy field at H ≥ 0.5HA. This is also illustrated by the smaller coercivity of Fe3O4 nanoparticles compared with that of their Fe counterparts. Therefore, understanding the interconnection between intrinsic parameters (composition, size and magnetic properties), the dosage (concentration, volume) and the intensity and frequency of the AC field can lead to essential design guidelines for in vitro, in vivo, and clinical applications of magnetic nanoparticles for hyperthermia.
Computational model of deformable lenses actuated by dielectric elastomers
Authors: Lu Tongqing , Cai Shengqiang , Wang Huiming , Suo Zhigang
Published: September 2013

A recent design of deformable lens mimics the human eye, adjusting its focal length in response to muscle-like actuation. The artificial muscle is a membrane of a dielectric elastomer subject to a voltage. Here, we calculate the coupled and inhomogeneous deformation of the lens and the dielectric elastomer actuator by formulating a nonlinear boundary-value problem. We characterize the strain-stiffening elastomer with the Gent model and describe the voltage-induced deformation using the model of ideal dielectric elastomer. The computational predictions agree well with experimental data. We use the model to explore the space of parameters, including the prestretch of the membrane, the volume of the liquid in the lens, and the size of the dielectric elastomer actuator relative to the lens. We examine how various modes of failure limit the minimum radius of curvature.
Orientation dependence of piezoelectric properties and mechanical quality factors of 0.27Pb(In1/2Nb1/2)O3-0.46Pb(Mg1/3Nb2/3)O3-0.27PbTiO3:Mn single crystals
Authors: Zheng Limei , Sahul Raffi , Zhang Shujun , Jiang Wenhua , Li Shiyang , Cao Wenwu
Published: September 2013

The complete set of material constants of single domain rhombohedral phase 0.27Pb(In1/2Nb1/2)O3-0.46Pb(Mg1/3Nb2/3)O3-0.27PbTiO3:Mn single crystal has been determined. The orientation dependence of piezoelectric, dielectric, and electromechanical properties was calculated based on these single domain data. The maximum piezoelectric and electromechanical properties were found to exist near the [001]C pseudo-cubic direction. In addition, the piezoelectric properties of [001]C poled crystals with “4R” multi-domain configuration were experimentally measured and compared with the calculated values. Only a small difference (3%) was found between experimental and theoretical values, indicating the high piezoelectric properties in the “4R” state are mainly from intrinsic contributions. The mechanical quality factors Q33 are significantly improved by the Mn-doping for the “4R” domain engineered crystals but almost no change for the single domain “1R” state. On the other hand, Q15 of both single domain and multidomain crystals were found to increase with Mn-doping, due to the internal bias induced by acceptor dopants, which clamps the domain wall motions and restricts polarization rotation.
Super-thin single crystal diamond membrane radiation detectors
Authors: Pomorski Michal , Caylar Benoit , Bergonzo Philippe
Published: September 2013

We propose to use the non-electronic grade (nitrogen content 5 ppb < [N] < 5 ppm) single crystal (sc) chemical vapour deposited (CVD) diamond as a thin-membrane radiation detector. Using deep Ar/O2 plasma etching it is possible to produce self-supported few micrometres thick scCVD membranes of a size approaching 7 mm × 7 mm, with a very good surface quality. After metallization and contacting, electrical properties of diamond membrane detectors were probed with 5.486 MeV α-particles as an ionization source. Despite nitrogen impurity, scCVD membrane detectors exhibit stable operation, charge collection efficiency close to 100%, with homogenous response, and extraordinary dielectric strength up to 30 V/μm.
A predictive model for thermodynamic stability of grain size in nanocrystalline ternary alloys
Authors: Saber Mostafa , Kotan Hasan , Koch Carl C. , Scattergood Ronald O.
Published: September 2013

This work presents a model for evaluating thermodynamic stabilization of ternary nanocrystalline alloys. It is applicable to alloy systems containing strongly segregating size-misfit solutes with a significant enthalpy of elastic strain and/or immiscible solutes with a positive mixing enthalpy. On the basis of a regular solution model, the chemical and elastic strain energy contributions are incorporated into the mixing enthalpy ΔHmix, and the mixing entropy ΔSmix is obtained using the ideal solution approximation. The Gibbs mixing free energy ΔGmix is minimized with respect to simultaneous variations in grain size and solute segregation parameters. The Lagrange multiplier method is used to obtain numerical solutions for the minimum ΔGmix corresponding to an equilibrium grain size for given alloy compositions. The numerical solutions will serve as a guideline for choosing solutes and assessing the possibility of thermodynamic stabilization. The temperature dependence of the nanocrystalline grain size and interfacial solute excess can be evaluated for selected ternary systems. Model predictions are presented using available input data for a wide range of solvent-solute combinations. The model predictions are compared to experimental results for Cu-Zn-Zr, Fe-Cr-Zr, and Fe-Ni-Zr alloys where thermodynamic stabilization might be effective.
Impact of the Sb content on the performance of GaAsSb-capped InAs/GaAs quantum dot lasers
Authors: Utrilla A. D. , Ulloa J. M. , Guzman A. , Hierro A.
Published: September 2013

Type I and type II band alignment InAs/GaAs quantum dot laser diodes (LD) are demonstrated using a 5-nm-thick GaAsSb capping layer with moderate or high Sb contents. The threshold current density, external differential quantum efficiency, and characteristic temperature substantially improve when Sb is used in the capping layer. Nevertheless, in the type II LD, lasing arises from type I-like excited states with much shorter lasing wavelengths than expected. This is likely related to the observed inhibition of the ground state transition in the spontaneous emission, which would also reduce the radiative current and, therefore, the threshold current.
Characterization of full set material constants of piezoelectric materials based on ultrasonic method and inverse impedance spectroscopy using only one sample
Authors: Li Shiyang , Zheng Limei , Jiang Wenhua , Sahul Raffi , Gopalan Venkatraman , Cao Wenwu
Published: September 2013

The most difficult task in the characterization of complete set material properties for piezoelectric materials is self-consistency. Because there are many independent elastic, dielectric, and piezoelectric constants, several samples are needed to obtain the full set constants. Property variation from sample to sample often makes the obtained data set lack of self-consistency. Here, we present a method, based on pulse-echo ultrasound and inverse impedance spectroscopy, to precisely determine the full set physical properties of piezoelectric materials using only one small sample, which eliminated the sample to sample variation problem to guarantee self-consistency. The method has been applied to characterize the [001]C poled Mn modified 0.27Pb(In1/2Nb1/2)O3-0.46Pb(Mg1/3Nb2/3)O3-0.27PbTiO3 single crystal and the validity of the measured data is confirmed by a previously established method. For the inverse calculations using impedance spectrum, the stability of reconstructed results is analyzed by fluctuation analysis of input data. In contrast to conventional regression methods, our method here takes the full advantage of both ultrasonic and inverse impedance spectroscopy methods to extract all constants from only one small sample. The method provides a powerful tool for assisting novel piezoelectric materials of small size and for generating needed input data sets for device designs using finite element simulations.
Alternating current-generated plasma discharges for the controlled direct current charging of ferroelectrets
Authors: Cury Basso Heitor , Monteiro José Roberto B. de A. , Baladelli Mazulquim Daniel , Teixeira de Paula Geyverson , Gonçalves Neto Luiz , Gerhard Reimund
Published: September 2013

The standard charging process for polymer ferroelectrets, e.g., from polypropylene foams or layered film systems involves the application of high DC fields either to metal electrodes or via a corona discharge. In this often-used process, the DC field triggers the internal breakdown and limits the final charge densities inside the ferroelectret cavities and, thus, the final polarization. Here, an AC + DC charging procedure is proposed and demonstrated in which a high-voltage high-frequency (HV-HF) wave train is applied together with a DC poling voltage. Thus, the internal dielectric-barrier discharges in the ferroelectret cavities are induced by the HV-HF wave train, while the final charge and polarization level is controlled separately through the applied DC voltage. In the new process, the frequency and the amplitude of the HV-HF wave train must be kept within critical boundaries that are closely related to the characteristics of the respective ferroelectrets. The charging method has been tested and investigated on a fluoropolymer-film system with a single well-defined cylindrical cavity. It is found that the internal electrical polarization of the cavity can be easily controlled and increases linearly with the applied DC voltage up to the breakdown voltage of the cavity. In the standard charging method, however, the DC voltage would have to be chosen above the respective breakdown voltage. With the new method, control of the HV-HF wave-train duration prevents a plasma-induced deterioration of the polymer surfaces inside the cavities. It is observed that the frequency of the HV-HF wave train during ferroelectret charging and the temperature applied during poling of ferroelectrics serve an analogous purpose. The analogy and the similarities between the proposed ferroelectret charging method and the poling of ferroelectric materials or dipole electrets at elevated temperatures with subsequent cooling under field are discussed.
Plasmonic Au nanoparticles on 8 nm TiO2 nanotubes for enhanced photocatalytic water splitting
Authors: Kim Hyunsu , Choi Chulmin , Khamwannah Jirapon , Young Noh Sun , Zhang Yanyan , Seong Tae-Yeon , Jin Sungho
Published: September 2013

We report here for the first time a successful distribution and attachment of fine Au nanoparticles on ∼8 nm diameter TiO2 nanotubes having significantly increased surface area. Au thin film deposition onto hydrothermally grown TiO2 nanotube arrays followed by thermal annealing breaks up the Au film into desired, uniformly distributed nanoparticles. Visible light absorption spectra of the gold nanoparticles on TiO2 nanotubes indicate that the Au nanoparticles are photo-excited due to plasmon resonance, and charge separation is accomplished by the transfer of photoexcited electrons from the gold particle to the TiO2 conduction band, thereby enhancing photoelectrochemical performance. By virtue of substantially increased surface area with the 8 nm TiO2 nanotube substrate in combination with the plasmonic effect of distributed Au nanoparticles, significantly increased photocurrent density was obtained with extended light absorbance from the UV regime to the visible spectrum region. Such gold nanoparticle decorated, fine TiO2 nanostructures fabricated by a simple and versatile method can be useful for hydrogen generation by water splitting, CO oxidation and various other types of photocatalysts and photovoltaic fuel cells.
Tunable two types of Fano resonances in metal–dielectric core–shell nanoparticle clusters
Authors: Yang Zhong-Jian , Wang Qu-Quan , Lin Hai-Qing
Published: September 2013

We demonstrate that two types of Fano resonances could be observed in metal–dielectric core–shell nanoparticle heptamer clusters. The first kind of Fano resonance is caused by the coupling between electric dipolar plasmon modes. It still remains with high refractive index shells even though metal cores are separated by them. The second one is caused by the interference between scattering electromagnetic modes of dielectric shell and modified plasmon modes. The energy and line shape of these Fano resonances are highly tunable with shell index and particle geometry, which could find applications in nanophotonics.
Optimization of microbial oils production from kitchen garbage by response surface methodology
Authors: Cao Yuanyuan , Yao Jianming , Li Jun , Chen Xiangsong , Wu Jinyong
Published: September 2013

To reuse kitchen garbage for microbial oils, increase the liquid yield, and reduce the production cost, response surface methodology based on Box-Behnken design was employed to identify the optimum conditions for microbial oils production from kitchen garbage by the Geotrichum robustum G9 strain. Experimental results showed that the theoretical maximum lipid yield of 9.89 g/l was obtained with the following optimum conditions: time at 7.55 days, pH at 6.16, and temperature at 28 °C, when the lipid yield could reach 20 kg per ton of kitchen garbage. Analysis results on fatty acids composition and relative content by gas chromatography and mass spectrometry showed that the lipid in strain G9 cultured by kitchen garbage was mainly composed of 16-carbon and 18-carbon fatty acids. Such compositional features were similar to plant oil, the widely used feedstock for biodiesel at present. Kitchen garbage could be considered as ideal substrate for the G. robustum G9 strain for biodiesel production. The utilization of kitchen garbage for microbial oils production could reduce cost as well as reduce pollution.
Burning Desires: Untangling and Interpreting ‘Pro-Poor’ Biofuel Policy Processes in India and South Africa
Authors: Pradhan Shishusri , Ruysenaar Shaun
Published: September 2013

The bio-economy is characterised by aspirations of replacing the fossil-based economy with biobased energy, resources and processes; biofuels are particularly popular. This new shift comes with multiple risks and uncertainties in both industrialised and developing economies. The uptake of biofuels is inextricably linked to and legitimised by policy processes involving a complicated nexus of vested interests, political aspirations, and technological drivers, and a range of associated factors. In this paper we describe the characteristics of and contours along which two national biofuels policies in India and South Africa have been articulated and developed. In doing so we establish how a biofuels regime has gained legitimacy, becoming embedded into policy processes dictated largely through specific networks and reflective of the rationalising effect of global and local narratives. We analyse how pro-poor ‘win-win’ narratives gained purchase amongst different actors and in turn how they were used as a basis for biofuels policies. The case studies are, however, complex and differentiated, pointing towards sociopolitical nuances and structural subtleties.
Composition of water-soluble organic carbon in non-urban atmospheric aerosol collected at the Storm Peak Laboratory
Authors: Samburova Vera , Hallar A. Gannet , Mazzoleni Lynn R. , Saranjampour Parichehr , Lowenthal Douglas , Kohl Steven D. , Zielinska Barbara
Published: September 2013

Environmental context The organic fraction of atmospheric aerosols is a complex mixture of thousands of species, which play an important role in many atmospheric processes, such as absorbing and scattering solar radiation. We analysed the water-soluble organic fraction of ambient aerosol samples, and quantified over 45 carboxylic acids, sugars, sugar anhydrides and sugar alcohols. The presence of fairly high concentrations of sugars and sugar-alcohols suggests a significant biological input (e.g. pollen, fungi and bacteria) to the water-soluble organic fraction of non-urban aerosols. Abstract Water-soluble organic constituents of PM2.5 aerosol (particulate matter with an aerodynamic diameter ≤2.5µm) have not been well characterised so far. The goal of this work was to perform quantitative analysis of individual water-soluble organic species in aerosol samples collected in July of 2010 at the Storm Peak Laboratory (3210m above sea level) located in the Colorado Park Range (Steamboat Springs, CO, USA). Aqueous extracts were combined into six composites and analysed for organic carbon (OC), water-soluble organic carbon (WSOC), water-insoluble OC, inorganic ions, organic acids, lignin derivatives, sugar-alcohols, sugars and sugar-anhydrates. Analysis of higher molecular weight water-soluble organics was done using ultrahigh resolution mass spectrometry. Approximately 2400 positive and 4000 negative ions were detected and assigned to monoisotopic molecular formulae in the mass range of 100–800Da. The higher number of negative ions reflects a predominant presence of highly oxidised organic compounds. Individual identified organic species represented up to 30% of the water-soluble organic mass (WSOM). The WSOM fractions of the low molecular weight organic acids, sugars and sugar alcohols were 3–12%, 1.0–16% and 0.4–1.9%. Significant amounts of arabitol, mannitol and oxalic acid are most likely associated with airborne fungal spores and conidia that were observed on the filters using high resolution electron microscopy. Overall, higher concentrations of sugars (glucose, sucrose, fructose etc.) in comparison with biomass burning tracer levoglucosan indicate that a significant mass fraction of WSOC is related to airborne biological species.
Grass height is the determinant of sheep grazing effects on small mammals in a savanna ecosystem
Authors: Kuiper T. R. , Parker D. M.
Published: September 2013

Small mammals play an important role in many ecosystems; hence, the factors that influence their community structure are of interest. Ungulate grazing is one such factor, and this study focussed on the effect of sheep (Ovis aries) grazing in a savanna ecosystem on small-mammal community structure. In a landscape-scale assessment, small-mammal community structure was compared at three different levels of grazing on a sheep farm in the Sub-Escarpment Savanna of the Eastern Cape, South Africa. In total, 97 small-mammal individuals across seven species were trapped. Of these individuals, 81.4% were trapped on the no-grazing control, whereas 15.5% and 3.1% were trapped on the medium- and high-grazing treatments, respectively. The results showed that the only significant differences in abundance, diversity, evenness, and richness of small mammals among grazing treatments were those mediated by the effect of grazing on grass height. It is proposed that the reduction in grass height associated with grazing is the primary mechanism by which sheep adversely affect small mammals in this ecosystem. This could be explained by the increased exposure of small mammals to predators after grazing of grass by sheep, and food competition between sheep and small mammals. The data also suggest that small mammals may persist in small and isolated patches of suitable habitat (long grass) within heavily grazed pastures subjected to rotational grazing. In the broader context of community ecology, this study sheds light on cryptic and dynamic interactions between two quite different grazing guilds. Experimental work of this kind may help to determine the role of introduced sheep in biodiversity loss of small mammals across the globe.
Functional role of oligomerization for bacterial and plant SWEET sugar transporter family
Authors: Xuan Yuan Hu , Hu Yi Bing , Chen Li-Qing , Sosso Davide , Ducat Daniel C. , Hou Bi-Huei , Frommer Wolf B.
Published: September 2013

Significance

SWEET sugar transporter homologs from bacteria were identified and named SemiSWEETs. They are small proteins with only three transmembrane domains (TMs); they are too small to create pores by themselves, but likely, they assemble multiple 3-TMs into a complex. SemiSWEETs are related to SWEETs, which play important roles in intercellular and interorgan sugar translocation in plants, and they are found in animals. SWEETs have fused two 3-TM units through a linker. However, SWEETs seem to be too small to transport sugars on their own. Here, we show that SWEET function requires assembly into oligomers, indicating that a pore requires at least an SWEET dimer.
Readability revisited? The implications of text complexity
Authors: Wray David , Janan Dahlia
Published: September 2013

The concept of readability has had a variable history, moving from a position where it was considered as a very important topic for those responsible for producing texts and matching those texts to the abilities and needs of learners, to its current declining visibility in the education literature. Some important work has been coming from the USA over the past few years, however, which makes it clear that a closer look at the text dimension of the reader–text interface is somewhat overdue. The issue has been redefined as one of text complexity, and there are some significant implications within it for the teaching and development of reading at all phases of learning. In this paper, we try to review some of these implications and suggest their relevance to the UK situation.
Plasma membrane organization and function: moving past lipid rafts
Authors: Kraft Mary L.
Published: September 2013

“Lipid raft” is the name given to the tiny, dynamic, and ordered domains of cholesterol and sphingolipids that are hypothesized to exist in the plasma membranes of eukaryotic cells. According to the lipid raft hypothesis, these cholesterol- and sphingolipid-enriched domains modulate the protein–protein interactions that are essential for cellular function. Indeed, many studies have shown that cellular levels of cholesterol and sphingolipids influence plasma membrane organization, cell signaling, and other important biological processes. Despite 15 years of research and the application of highly advanced imaging techniques, data that unambiguously demonstrate the existence of lipid rafts in mammalian cells are still lacking. This Perspective summarizes the results that challenge the lipid raft hypothesis and discusses alternative hypothetical models of plasma membrane organization and lipid-mediated cellular function.
Grapevine Trunk Diseases in British Columbia: Incidence and Characterization of the Fungal Pathogens Associated with Black Foot Disease of Grapevine
Authors: Úrbez-Torres J. R. , Haag P. , Bowen P. , O'Gorman D. T.
Published: September 2013

Black foot disease of grapevines, caused by several fungal species in the genera Campylocarpon, Cylindrocarpon, Cylindrocladiella, and Ilyonectria, causes significant economic losses to the grapevine industry worldwide. This study represents the first attempt to identify and characterize the fungal pathogens associated with black foot disease of grapevines in British Columbia (BC). Field surveys conducted throughout all grape-growing regions in BC that included assessment of foliar symptomatology and isolations from symptomatic vines showed Cylindrocarpon/Ilyonectria spp. occurred in 32 of 90 (35.5%) young vineyards surveyed (≤8 year old) and in 41 of 215 (19%) samples collected. In 20 of the 41 (48.8%) samples, Cylindrocarpon/Ilyonectria spp. were the sole fungi isolated from symptomatic tissue. In the rest of the samples, black foot fungi were found to primarily coexist with fungal taxa associated with Petri disease of grapevines. Colony and conidia phenotypical characterization, along with DNA analyses of the internal transcribed spacer region (ITS1-5.8S-ITS2) of the rDNA, and part of the β-tubulin and translation elongation factor 1-α genes, revealed five different black foot fungi occurring in declining young vines in BC, namely Cylindrocarpon pauciseptatum, Ilyonectria liriodendri, Ilyonectria macrodidyma, Ilyonectria robusta, and Ilyonectria torresensis. Pathogenicity studies showed all five species to be highly virulent in the grapevine rootstock cultivar 3309C. Overall, I. liriodendri and I. macrodidyma were the most virulent species when inoculated in Vitis vinifera ‘Chardonnay’ and rootstock 3309C.