bluuebunny/crossref_metadata_2025 huggingface dataset:
Laminar flow of a viscoelastic shear-thinning liquid over a backward-facing step preceded by a gradual contraction
Authors: Poole R. J. , Escudier M. P. , Afonso A. , Pinho F. T.
Published: September 2007

Experimental observations and numerical simulations, based upon the Phan-Thien and Tanner model, are reported for the laminar flow of a series of viscoelastic liquids (0.05%, 0.1%, and 0.4% concentrations of a polyacrylamide) over a symmetrical, double backward-facing step geometry preceded by a short gradual contraction from a long (120 hydraulic diameters in length) square duct. Reynolds numbers are typically between 10 and 100 (i.e., inertia is not negligible) and Deborah numbers of order 100 for the experiments (based on a relaxation time determined from linear viscoelasticity measurements) and order 10 for the viscoelastic simulations. As the polymer concentration is increased, the combined effects of increased shear thinning and viscoelasticity are found to dramatically reduce the length of the recirculation region downstream of the step. The nature of the flow field within the contraction itself is found to be fundamentally different for the viscoelastic liquids to that for a comparable Newtonian fluid flow: large velocity overshoots with very strong gradients appear near to the sidewalls that, due to their appearance, we have dubbed “cat’s ears.” The simulations are able to reproduce these remarkable features, at least qualitatively.
Dissociation energy of the water dimer from quantum Monte Carlo calculations
Authors: Gurtubay I. G. , Needs R. J.
Published: September 2007

We report a study of the electronic dissociation energy of the water dimer using quantum Monte Carlo techniques. We have performed variational quantum Monte Carlo and diffusion quantum Monte Carlo (DMC) calculations of the electronic ground state of the water monomer and dimer using all-electron and pseudopotential approaches. We have used Slater-Jastrow trial wave functions with B3LYP type single-particle orbitals, into which we have incorporated backflow correlations. When backflow correlations are introduced, the total energy of the water monomer decreases by about 4–5mhartree, yielding a DMC energy of −76.42830(5)hartree, which is only 10mhartree above the experimental value. In our pseudopotential DMC calculations, we have compared the total energies of the water monomer and dimer obtained using the locality approximation with those from the variational scheme recently proposed by Casula [Phys. Rev. B 74, 161102–R (2006)]. The time step errors in the Casula scheme are larger, and the extrapolation of the energy to zero time step always lies above the result obtained with the locality approximation. However, the errors cancel when energy differences are taken, yielding electronic dissociation energies within error bars of each other. The dissociation energies obtained in our various all-electron and pseudopotential calculations range between 5.03(7) and 5.47(9)kcal∕mol and are in good agreement with experiment. Our calculations give monomer dipole moments which range between 1.897(2) and 1.909(4)D and dimer dipole moments which range between 2.628(6) and 2.672(5)D.
Pair potential for helium from symmetry-adapted perturbation theory calculations and from supermolecular data
Authors: Jeziorska Małgorzata , Cencek Wojciech , Patkowski Konrad , Jeziorski Bogumił , Szalewicz Krzysztof
Published: September 2007

Symmetry-adapted perturbation theory (SAPT) was applied to the helium dimer for interatomic separations R from 3to12bohrs. The first-order interaction energy and the bulk of the second-order contribution were obtained using Gaussian geminal basis sets and are converged to about 0.1mK near the minimum and for larger R. The remaining second-order contributions available in the SAPT suite of codes were computed using very large orbital basis sets, up to septuple-zeta quality, augmented by diffuse and midbond functions. The accuracy reached at this level was better than 1mK in the same region. All the remaining components of the interaction energy were computed using the full configuration interaction method in bases up to sextuple-zeta quality. The latter components, although contributing only 1% near the minimum, have the largest uncertainty of about 10mK in this region. The total interaction energy at R=5.6bohrs is −11.000±0.011K. For R⩽6.5bohrs, the supermolecular (SM) interaction energies computed by us recently turned out to be slightly more accurate. Therefore, we have combined the SM results for R⩽6.5bohrs with the SAPT results from 7.0to12bohrs to fit analytic functions for the potential and for its error bars. The potential fit uses the best available van der Waals constants C6 through C16, including C11, C13, and C15, and is believed to be the best current representation of the Born-Oppenheimer (BO) potential for helium. Using these fits, we found that the BO potential for the helium dimer exhibits the well depth De=11.006±0.004K, the equilibrium distance Re=5.608±0.012bohrs, and supports one bound state for He24 with the dissociation energy D0=1.73±0.04mK, and the average interatomic separation ⟨R⟩=45.6±0.5Å.
Exploring transmembrane transport through α-hemolysin with grid-steered molecular dynamics
Authors: Wells David B. , Abramkina Volha , Aksimentiev Aleksei
Published: September 2007

The transport of biomolecules across cell boundaries is central to cellular function. While structures of many membrane channels are known, the permeation mechanism is known only for a select few. Molecular dynamics (MD) is a computational method that can provide an accurate description of permeation events at the atomic level, which is required for understanding the transport mechanism. However, due to the relatively short time scales accessible to this method, it is of limited utility. Here, we present a method for all-atom simulation of electric field-driven transport of large solutes through membrane channels, which in tens of nanoseconds can provide a realistic account of a permeation event that would require a millisecond simulation using conventional MD. In this method, the average distribution of the electrostatic potential in a membrane channel under a transmembrane bias of interest is determined first from an all-atom MD simulation. This electrostatic potential, defined on a grid, is subsequently applied to a charged solute to steer its permeation through the membrane channel. We apply this method to investigate permeation of DNA strands, DNA hairpins, and α-helical peptides through α-hemolysin. To test the accuracy of the method, we computed the relative permeation rates of DNA strands having different sequences and global orientations. The results of the G-SMD simulations were found to be in good agreement in experiment.
Shallow acceptors in GaN
Authors: Eberlein T. A. G. , Jones R. , Öberg S. , Briddon P. R.
Published: September 2007

Recent high resolution photoluminescence studies of high quality Mg doped GaN show the presence of two acceptors. One is due to Mg and the other labeled A1 has a shallower acceptor defect. The authors investigate likely candidates for this shallow acceptor and conclude that CN is the most likely possibility. The authors also show that the CN is passivated by H and the passivated complex is more stable than MgGa–H.
Orbital currents in the Colle-Salvetti correlation energy functional and the degeneracy problem
Authors: Pittalis S. , Kurth S. , Sharma S. , Gross E. K. U.
Published: September 2007

Popular density functionals for the exchange-correlation energy typically fail to reproduce the degeneracy of different ground states of open-shell atoms. As a remedy, functionals which explicitly depend on the current density have been suggested. We present an analysis of this problem by investigating functionals that explicitly depend on the Kohn-Sham orbitals. Going beyond the exact-exchange approximation by adding correlation in the form of the Colle-Salvetti functional, we show how current-dependent terms enter the Colle-Salvetti expression and their relevance is evaluated. A very good description of the degeneracy of ground states for atoms of the first and second rows of the Periodic Table is obtained.
Wide bandwidth transimpedance amplifier for extremely high sensitivity continuous measurements
Authors: Ferrari Giorgio , Sampietro Marco
Published: September 2007

This article presents a wide bandwidth transimpedance amplifier based on the series of an integrator and a differentiator stage, having an additional feedback loop to discharge the standing current from the device under test (DUT) to ensure an unlimited measuring time opportunity when compared to switched discharge configurations while maintaining a large signal amplification over the full bandwidth. The amplifier shows a flat response from 0.6Hzto1.4MHz, the capability to operate with leakage currents from the DUT as high as tens of nanoamperes, and rail-to-rail dynamic range for sinusoidal current signals independent of the DUT leakage current. Also available is a monitor output of the stationary current to track experimental slow drifts. The circuit is ideal for noise spectral and impedance measurements of nanodevices and biomolecules when in the presence of a physiological medium and in all cases where high sensitivity current measurements are requested such as in scanning probe microscopy systems.
Dirichlet extremum problem associated with the asymmetric grain-boundary thermal grooving under the Dirac δ-type anisotropic surface stiffness in bicrystal thin solid films
Authors: Ogurtani Tarik Omer
Published: September 2007

A generalized Rayleigh-Ritz (RR) method combined with the Galerkin (RRG) functional space approximation is elaborated by using the extended and modified Laguerre functions manifold for the weak solution of the asymmetric grain-boundary thermal grooving problem with the Dirichlet boundary. This new hybrid RRG approach, which resembles the front-tracking method, reveals the fine features of the grain boundary groove-root topography (rough or faceted regions) more accurately than the previous approach under the severe nonanalyticity of the surface stiffness anisotropy, and showing almost excellent in accord with the experimental observations made by atomic force microscopy and scanning tunneling microscopy. The large deviations from Mullins’ t1/4 scaling law combined with the self-trapping (quasifaceting) are observed especially at low values of the normalized longitudinal mobilities, where the kinetics rather than the energetic considerations are found to be the dominating factor for the whole topographic appearances. For very high longitudinal mobilities, the smooth and symmetric groove profiles (no faceting) are found to be represented by the Mullins’ function for the fourfold symmetry in the stationary state with great precision, if one modifies the rate parameter by the anisotropy constant and simultaneously utilizes the anisotropic complementary dihedral angle in the calculation of the slope parameter. A recently developed analytical theory fully supports this observation rigorously, and furnishes the quantitative determination of the threshold level of the anisotropy constant for the ridge formation, and as well as the penetration depth evaluation.
Anisotropic form of third-order moments and relationship to the cascade rate in axisymmetric magnetohydrodynamic turbulence
Authors: Podesta J. J. , Forman M. A. , Smith C. W.
Published: September 2007

Laws governing the behavior of statistical third-order moments in the inertial range are among the few rigorous results in the theory of statistically homogeneous incompressible magnetohydrodynamic turbulence. These fundamental laws apply to both isotropic and anisotropic turbulence. Assuming that the turbulence is stationary in time and statistically axisymmetric under proper rotations about the direction of the mean magnetic field, it is shown that the general mathematical form of the tensor quantities appearing in these laws is constrained by symmetry to have a particular form. Using these forms, the general solutions of the law for the vector and pseudovector third-order moments F and FC are obtained in the limit of large kinetic Reynolds number and large magnetic Reynolds number. The physical meaning of the different terms in F and FC are investigated and a method for obtaining the cascade rates of energy ϵ and cross-helicity ϵC from experimental data is described. The results show that the measurement of the cascade rates goes hand-in-hand with the measurement of the spatial anisotropy of the third-order moments F and FC. The theory developed here can be applied to measure the turbulent cascade rates of energy and cross-helicity in laboratory plasma experiments, numerical simulations, and the solar wind.
Kirk effect mechanism in type-II InP∕GaAsSb double heterojunction bipolar transistors
Authors: Tao N. G. , Bolognesi C. R.
Published: September 2007

The Kirk effect mechanism is studied in type-II InP∕GaAsSb∕InP NpN double heterojunction bipolar transistors (DHBTs) both experimentally and through two-dimensional hydrodynamic numerical simulations. We show that the large valence band discontinuity ΔEV at the GaAsSb–InP base∕collector heterojunction does not allow hole injection into the InP collector as is the case in homojunction collectors. Instead, a blocking barrier is electrostatically induced in the base layer at high collector current densities: this barrier increases base recombination and decreases the current gain. We show that tunneling transport must be considered at the base∕collector heterojunction and that the induced barrier depends on the base layer doping level—effectively, InP∕GaAsSb DHBTs display high-current limitations that are also controlled to some extent by the base doping level.
Enhancement and angular dependence of transport critical current density in pulsed laser deposited YBa2Cu3O7−x+BaSnO3 films in applied magnetic fields
Authors: Varanasi C. V. , Burke J. , Brunke L. , Wang H. , Sumption M. , Barnes P. N.
Published: September 2007

Y Ba 2 Cu 3 O 7 − x (YBCO) films with nanoparticles of BaSnO3 (BSO) were processed using pulsed laser ablation of a special target made with dual phase sectors of YBCO and BSO. Transport critical current density (Jct) of these YBCO+BSO films in applied magnetic fields and angular dependence of Jct on the applied field orientation was measured. It was observed that in the YBCO+BSO films, the Jct (H‖c orientation) increased considerably as compared to regular YBCO films and was 1.3 times higher than Jct in H‖ab orientation. Cross-sectional transmission electron microscopy images on YBCO+BSO films showed the presence of high density (3.5×1011cm−2) of nanoparticles (∼10nm size) and nanocolumns that extended throughout the thickness of the films with high density of dislocations and stacking faults (1000μm−2). The observed results of enhancements in Jct in H‖c and Jct in H‖ab orientations were discussed in the light of the observed microstructural details.
The deviatoric response of an alumina filled epoxy composite during shock loading
Authors: Millett J. C. F. , Deas D. , Bourne N. K. , Montgomery S. T.
Published: September 2007

The deviatoric response of a particulate alumina-epoxy composite to shock loading has been investigated using manganin stress gauges sensitive to the lateral component of stress. Results show that the lateral stress and thus the shear strength are near constant behind the shock front, indicating that the presence of alumina has a diluting response of the epoxy resin. The shear strength has been observed to increase with increasing shock stress, in agreement with comparisons between the measured shock stress and the calculated hydrodynamic pressure. Finally, the Hugoniot elastic limit of this material has been estimated at ∼1.6GPa by the intersection between the elastic and inelastic shear strengths.
Integrable almost-symplectic Hamiltonian systems
Authors: Fassò Francesco , Sansonetto Nicola
Published: September 2007

We extend the notion of Liouville integrability, which is peculiar to Hamiltonian systems on symplectic manifolds, to Hamiltonian systems on almost-symplectic manifolds, namely, manifolds equipped with a nondegenerate (but not closed) 2-form. The key ingredient is to require that the Hamiltonian vector fields of the integrals of motion in involution (or equivalently, the generators of the invariant tori) are symmetries of the almost-symplectic form. We show that, under this hypothesis, essentially all of the structure of the symplectic case (from quasiperiodicity of motions to an analog of the action-angle coordinates and of the isotropic-coisotropic dual pair structure characteristic of the fibration by the invariant tori) carries over to the almost-symplectic case.
Critical temperatures in thermocompression gold stud bonding
Authors: Zhang G. G. , Ang X. F. , Chen Z. , Wong C. C. , Wei J.
Published: September 2007

A study on temperature dependence in gold-gold (Au–Au) thermocompression bonding was performed. Gold studs were bonded to two kinds of surfaces—cofired gold on alumina and electroless nickel covered with immersion Au on silicon. A critical bonding temperature was observed for both substrates. No bonding occurs when the temperature is below this threshold value, whereas bond strength increases with bonding temperature beyond the threshold. This critical temperature can be related to the activation of organic films on the bonding surfaces. Under similar bonding conditions, the critical temperature is lower for a harder substrate than for a softer substrate, primarily because of larger interfacial shear stresses. This is supported by the observation on the interfacial shear stress distribution at the bonding interface based on finite element simulation models of substrates with different hardness.
Radiation-induced decay of Shubnikov–de Haas oscillations in the regime of the radiation-induced zero-resistance states
Authors: Mani R. G.
Published: September 2007

Shubnikov–de Haas (SdH) oscillations decay under the influence of radiation in the regime of the radiation-induced zero-resistance states in GaAs∕AlGaAs devices. Experiment demonstrates that the SdH amplitude scales linearly with the average background resistance in the vicinity of the radiation-induced resistance minima, which shows that the SdH amplitude vanishes in proportion to the background resistance at the centers of the radiation-induced zero-resistance states.
A high-precision five-degree-of-freedom measurement system based on laser collimator and interferometry techniques
Authors: Kuang Cuifang , Hong En , Ni Jun
Published: September 2007

A novel sensitivity improving method for simultaneously measuring five-degree-of-freedom errors of a moving linear stage is proposed based on collimator and interferometry techniques. The measuring principle and parameters of the system are analyzed theoretically. The experimental results proved that the resolution of the linear displacement of the proposed method has twice that of the current linear interferometer, and the resolutions of the two-dimensional straightness error measurement can be improved by a factor of 8 compared with the movement of the retroreflector itself by using multireflection and lens magnification. The resolutions of the pitch and yaw angular error measurement have been improved by a factor of 10 compared with the rotation of the plane mirror itself by using expander lenses. The whole measuring system is characterized of simple structure, small volume, and high precision. The moving component of the measurement system is wireless, which eliminates the errors and inconvenience introduced by the wire connection. Calibration and comparison tests of this system compared with Renishaw laser interferometer system have been carried out. Experimental results show good consistency for measuring a linear guide way.
Bright white upconversion luminescence in rare-earth-ion-doped Y2O3 nanocrystals
Authors: Chen G. Y. , Liu Y. , Zhang Y. G. , Somesfalean G. , Zhang Z. G. , Sun Q. , Wang F. P.
Published: September 2007

Room temperature bright white upconversion (UC) luminescence in Yb3+–Tm3+–Er3+ ions doped Y2O3 nanocrystals was obtained under single-wavelength diode laser excitation of 976nm. The white light consists of the blue, green, and red UC radiations which correspond to the transitions G41→H63 of Tm3+, H11∕22∕S3∕24→I15∕24, and F9∕24→I15∕24 of Er3+ ions, respectively. The UC mechanisms were proposed based on spectral, kinetic, and pump power dependence analyses. The calculated color coordinates display that white light can be achieved in a wide range of pumping powers, which promises their potential applications in the field of displays, lasers, photonics, and biomedicine.
Electroforming and resistance-switching mechanism in a magnetite thin film
Authors: Odagawa A. , Katoh Y. , Kanzawa Y. , Wei Z. , Mikawa T. , Muraoka S. , Takagi T.
Published: September 2007

The electroforming and the resistance-switching behaviors in magnetite, Fe3O4, by the application of an appropriate electric field are demonstrated on a lateral device with multiple electrodes. By means of this device, both the location and the nature of the change in Fe3O4 are specified from the electrical measurements and Raman spectroscopy. The switching phenomenon is caused in maghemite, γ-Fe2O3, which is formed by oxidation of Fe3O4, near an interface of an anode. The authors argue that the switching motion is originated in a redox reaction between the Fe3O4 and γ-Fe2O3.
Conductivity type conversion in ion-milled p-HgCdTe:As heterostructures grown by molecular beam epitaxy
Authors: Izhnin I. I. , Dvoretsky S. A. , Mikhailov N. N. , Sidorov Yu. G. , Varavin V. S. , Mynbaev K. D. , Pociask M.
Published: September 2007

Conductivity type conversion in ion-milled As-doped p-HgCdTe heterostructures grown by molecular beam epitaxy on GaAs substrates has been studied. It was found that in these heterostructures, donor center concentration (∼1017cm−3) after ion milling was much higher than that could have been expected as a result of interaction of interstitial mercury atoms, generated under the milling, with the As acceptors. One possible reason of the donor center formation is the activation of an intrinsic neutral defect, which was present in the HgCdTe:As prior to the ion milling. The nature of the donor centers formed is discussed.
Polyaniline on crystalline silicon heterojunction solar cells
Authors: Wang Weining , Schiff E. A.
Published: September 2007

Organic/inorganic heterojunction solar cells were fabricated on the (100) face of n-type silicon crystals using acid-doped polyaniline (PANI) with widely varying conductivities. For films with conductivities below 10−1S∕cm, the open-circuit voltage VOC increases with increasing film conductivity as expected when VOC is limited by the work function of the film. Extrapolation of these results to the higher conductivity films indicates that PANI could support VOC of 0.7V or larger. VOC measurements for the cells with higher conductivity PANI saturated at 0.51V. We speculate that uncontrolled surface states at the PANI/Si interface are reducing these values.
Improvement of laser molecular beam epitaxy grown SrTiO3 thin film properties by temperature gradient modulation growth
Authors: Li Jin Long , Hao J. H. , Li Y. R.
Published: September 2007

Oxygen diffusion at the SrTiO3∕Si interface was analyzed. A method called temperature gradient modulation growth was introduced to control oxygen diffusion at the interface of SrTiO3∕Si. Nanoscale multilayers were grown at different temperatures at the initial growing stage of films. Continuous growth of SrTiO3 films was followed to deposit on the grown sacrificial layers. The interface and crystallinity of SrTiO3∕Si were investigated by in situ reflection high energy electron diffraction and x-ray diffraction measurements. It has been shown that the modulated multilayers may help suppress the interfacial diffusion, and therefore improve SrTiO3 thin film properties.
Ab initio study on intrinsic defect properties of germanium nitride considered for gate dielectric
Authors: Yang M. , Wang S. J. , Peng G. W. , Wu R. Q. , Feng Y. P.
Published: September 2007

First-principles calculations based on density-functional theory and local-density approximation were carried out to investigate intrinsic defect properties in β-Ge3N4. It was found that nitrogen vacancies are the main source of intrinsic defects in Ge3N4 due to their low formation energy. The N vacancies might become charge trapping centers since they induce energy levels near the Ge conduction band edge and in the middle of the Ge3N4 band gap. The formation energy of intrinsic defects in Ge3N4 is sensitive to N chemical potential, and N-rich ambient is favorable to reduce the concentration of N vacancies.
Two-glassy-phase bulk metallic glass with remarkable plasticity
Authors: Du X. H. , Huang J. C. , Hsieh K. C. , Lai Y. H. , Chen H. M. , Jang J. S. C. , Liaw P. K.
Published: September 2007

Using the computational-thermodynamic approach, the potential compositions of Zr–Cu–Ni–Al alloy system exhibiting the two-liquid miscibility phase equilibrium in the liquid temperature region have been identified. The resulting Zr base bulk metallic glasses show a microstructure of two microscaled glassy phases. The glass possesses a remarkable macroscopic plastic strain of 30% at room temperature. The gain of mechanical properties is attributed to the unique glassy structure correlated with the chemical inhomogeneity on the micron scale, the hard phases surrounded by the soft phases, leading extensive shear-band formation, interactions, and multiplication.
Low operating voltage bright organic light-emitting diode using iridium complex doped in 4,4′-bis[N-1-napthyl-N-phenyl-amino]biphenyl
Authors: Wang J. , Jiang Y. D. , Yu J. S. , Lou S. L. , Lin H.
Published: September 2007

A low driving voltage organic light-emitting diode using a yellow phosphor bis[2-(4-tert-butylphenyl)benzothiazolato-N,C2′] iridium (acetylacetonate) as a dopant and 4,4′-bis[N-1-napthyl-N-phenyl-amino]biphenyl as a host was fabricated. The device without p- or n-doped transporting layer shows a turn-on voltage as low as 2.45V, and a luminance of 1000cd∕m2 at 4.3V. A maximum luminance of 23230cd∕m2 at 10V was achieved. The decrease of the device turn-on voltage may result from direct charge carrier trapping in the dopant and hole only transporting characteristic of the host material. Both charge carrier trapping and energy transfer mechanisms were found in the electroluminescence process.
Bat wing airfoil and planform structures relating to aerodynamic cleanliness
Authors: Bullen R. D. , McKenzie N. L.
Published: September 2007

In this paper we examine 12 species of Western Australian bat for anatomical and morphometric attributes related to wing lift and drag characteristics. We present values for bat wing camber (typically 6.5–9%) and its location, measurements of wing planform and tip shape (typically elliptical but with two different tip designs), dimensions of wing leading-edge flaps (typically 8–10.5% of hand wing chord but with some species having much larger flaps up to 18%) and then discuss several features related to airflow separation control. All species assessed had thin, low-camber airfoil sections, an optimisation appropriate to the range of Reynolds Numbers in which bats fly. Wing relative cleanliness was consistent with, and functionally appropriate to, species foraging strategy. The interceptors had the point of maximum camber well forward and no trailing edge wing fences, optimisations for minimum drag generation. The air-superiority bats had leading-edge fences optimised for maximum lift generation while maintaining low drag. Surface bats were characterised by their low-aspect-ratio wingtips and the absence of optimisations for either low section drag or high lift. The frugivore and the carnivore appear to be discrete optimisations while the emballinurid had a long and broad leading edge flap in combination with a high-aspect-ratio tip. We propose a range of lift and drag coefficient values for use in models of metabolic power output.
Molecular-genetic analyses of dispersal and breeding behaviour in the Australian termite Coptotermes lacteus: evidence for non-random mating in a swarm-dispersal mating system
Authors: Thompson Graham J. , Lenz Michael , Crozier Ross H. , Crespi Bernard J.
Published: September 2007

We used microsatellite DNA markers to infer the dispersal and breeding behaviour of Coptotermes lacteus, a termite whose large mounds are a conspicuous feature of Australia’s central east coast. We genotyped a subsample of neuter offspring for each of 38 colonies sampled over two spatially separated populations, one in a natural forest and the other in an exotic radiata pine plantation. All colonies showed offspring genotype frequencies consistent with a single reproductive pair. This result confirms that stable monogamy is the normal breeding arrangement for this species and that multi-reproductive colonies are rare. The two study populations were significantly differentiated and the distance separating them (~150 km) is therefore an effective constraint on gene flow. The populations themselves, however, were not noticeably subdivided above the level of colony. This lack of within-population viscosity is unexpected for weakly dispersing species and suggests that local gamete dispersal is in fact quite effective in C. lacteus. Nonetheless, dispersing sexuals do not appear to mate randomly. Instead, all four microsatellite loci are deficient in heterozygotes, indicating that populations are substantially inbred, irrespective of habitat. Evidence from hierarchical F-statistics, spatial genetic autocorrelation and relatedness calculations suggests that deviations from Hardy–Weinberg equilibrium may result from either a preference for non-sibling relatives over totally unrelated mates, or from random mating with viscosity – though evidence for the latter hypothesis was not detected. These findings suggest that swarm-dispersal mating systems, usually considered to produce outbreeding and panmixia, can instead involve a notable degree of non-random mating.
Breeding behaviour and ecology of the grey fantail (Rhipidura albiscapa)
Authors: Munro Kat
Published: September 2007

The grey fantail (Rhipidura albiscapa) is a common Australian flycatcher, yet no detailed reports have been made of its breeding ecology. A population of grey fantails was studied over four seasons in the Australian Capital Territory. Males had large testes and pronounced cloacal protuberances, morphology suggestive of sperm competition. Although two polyandrous trios were observed, most individuals bred as part of a season-long monogamous pair, suggesting that extra-pair copulation may be the principal cause of sperm competition. Indeed, behavioural observations revealed that males regularly intruded other territories, targeting those with building, rather than incubating, females. Intruding males were observed harassing, attempting to copulate and successfully copulating with resident females. Males did not mate guard, but regularly attacked their mates during each building attempt. Despite the probability that extra-pair paternity is common in this species, grey fantails were monomorphic and monochromatic, with a high level of paternal care. Nest depredation was common, with 83% of all clutches depredated before fledging. High levels of male care in care in this species may be better explained by an increase in fledging success associated with high male contribution to offspring care than confidence of paternity.
Activity-related variation in blood parameters associated with oxygen transport and chronic stress in little penguins
Authors: Mortimer Louise , Lill Alan
Published: September 2007

Some birds facing energy ‘bottlenecks’ display elevated oxidative metabolism and oxygen delivery to tissues and could be particularly susceptible to chronic stress. We examined whether there was evidence for such trends in little penguins (Eudyptula minor) over the period from breeding to the post-moulting stage and particularly during the onshore moult-fast. Penguin parents contribute equally to incubation, brooding and brood provisioning. A few weeks post-breeding, adults undergo a protracted, terrestrial moult-fast and then make brief visits to the colony during the post-moulting stage. Provisioning nestling(s) and moulting could theoretically be particularly energetically and nutritionally demanding. We determined for adults whether mass, a body condition index and blood parameters influencing vascular oxygen carrying capacity (hematocrit, Hct; whole blood haemoglobin, Hb) and indicating chronic stress (leukocyte count, WBC; heterophil/lymphocyte ratio, H/L) varied from August to May in a manner reflecting likely variation in energy and nutrient demand. Female mass and body condition index decreased significantly between the incubation and guard stages, before returning to incubation levels between the guard and post-guard nestling stages. Both parameters declined to their lowest levels between the post-guard and moult stages, before increasing to levels comparable with those during nestling care between the moult and post-moult stages. Blood parameters in both sexes exhibited temporal variation similar to that in female mass and body condition index, declining to their lowest levels during moult and increasing after the moult to levels comparable with those during breeding. Results indicated that the period of most intense provisioning of nestlings was associated with a decrease in blood oxygen carrying capacity, but no pronounced change in chronic stress indicators. However, the penguin’s moult-fast involved a loss of female body condition and, in both sexes, a reduction in body mass, vascular oxygen carrying capacity and possibly specific immune competence. Thus, regulation of human disturbance in accessible little penguin colonies may be particularly important during moult.
Changes in tissue nucleic acid content and mucosal morphology during intestinal development in pouch young of the tammar wallaby (Macropus eugenii eugenii)
Authors: Lentle R. G. , Mellor D. J. , Hulls C. , Birtles M. , Moughan P. J. , Stafford K. J.
Published: September 2007

DNA and RNA content and the timing of development of various histological features in the small and large intestine of in-pouch tammar wallabies (Macropus eugenii eugenii) of various ages were measured. A significant decline in gut tissue DNA concentrations and increase in the RNA/DNA ratios over 300 days postpartum indicated that the early postnatal increase in gut tissue mass resulted largely from hypertrophy. Mean duodenal and ileal villus height and crypt depth were significantly greater for in-pouch young aged >100 days compared with those <100 days and were significantly greater in the duodenum than in the ileum. Goblet cells appeared more slowly during development and were fewer in number in the duodenal than in the colonic mucosa. The numbers of mucin-secreting duodenal goblet cells were greater in pouch young aged >100 days than in young aged <100 days. The colonic mucosa exhibited no villi or villus-like folds. Colonic crypt depth increased uniformly with age.
Reproductive anatomy, gonad development and spawning seasonality of nurseryfish, Kurtus gulliveri (Perciformes:Kurtidae)
Authors: Berra T. M. , Gomelsky B. , Thompson B. A. , Wedd D.
Published: September 2007

The nurseryfish, Kurtus gulliveri, of northern Australia, is remarkable for the fact that the males carry the egg mass on a supraoccipital hook on their forehead. Plankton samples of larval nurseryfish indicate a prolonged spawning season (June–November) that more or less corresponds with the dry season in the Northern Territory. The paired, elongate testes are located in the posterior portion of the body cavity suspended by the mesorchium. The gonadosomatic index (GSI) of males was small and highly variable (mean 0.14, range 0.01–0.27) from June to November. The histological structure of testicular lobes showed maturing and mature stages that contained spermatocytes, spermatids, and spermatozoa. The paired, bean-shaped ovaries contained about 5500 oocytes (1176–9783) and were located in the rear of the abdominal cavity. GSI averaged 1.58 (range 0.36–4.48). Ovarian histology revealed primary growth, cortical alveolar oocytes, vitellogenic oocytes, coalesced yolk, and atresia. The occurrence of postovulatory follicles and late vitellogenetic oocytes in the ovaries clearly indicate that nurseryfish females are batch spawners. Maturing testes showed signs of previous spawnings indicating that males are capable of spawning several times throughout the spawning season. We speculate that nurseryfish may spawn in a manner similar to their closest relatives, cardinalfishes (Apogonidae), with eggs carried on the male’s hook instead of orally.
Evolution of asexual reproduction in leaves of the genus
Kalanchoë
Authors: Garcês Helena M. P. , Champagne Connie E. M. , Townsley Brad T. , Park Soomin , Malhó Rui , Pedroso Maria C. , Harada John J. , Sinha Neelima R.
Published: September 2007

Plant somatic cells have the remarkable ability to regenerate an entire organism. Many species in the genus
Kalanchoë
, known as “mother of thousands,” develop plantlets on the leaf margins. Using key regulators of organogenesis (
STM
) and embryogenesis (
LEC1
and
FUS3
) processes, we analyzed asexual reproduction in
Kalanchoë
leaves. Suppression of
STM
abolished the ability to make plantlets. Here, we report that constitutive plantlet-forming species, like
Kalanchoë daigremontiana
, form plantlets by coopting both organogenesis and embryogenesis programs into leaves. These species have a defective
LEC1
gene and produce nonviable seed, whereas species that produce plantlets only upon stress induction have an intact
LEC1
gene and produce viable seed. The latter species are basal in the genus, suggesting that induced-plantlet formation and seed viability are ancestral traits. We provide evidence that asexual reproduction likely initiated as a process of organogenesis and then recruited an embryogenesis program into the leaves in response to loss of sexual reproduction within this genus.
Increased motion and travel, rather than stable docking, characterize the last moments before secretory granule fusion
Authors: Degtyar Vadim E. , Allersma Miriam W. , Axelrod Daniel , Holz Ronald W.
Published: September 2007

The state of secretory granules immediately before fusion with the plasma membrane is unknown, although the granules are generally assumed to be stably bound (docked). We had previously developed methods using total internal reflection fluorescence microscopy and image analysis to determine the position of chromaffin granules immediately adjacent to the plasma membrane with high precision, often to within ≈10 nm, or <5% of the granule diameter (300 nm). These distances are of the dimensions of large proteins and are comparable with the unitary step sizes of molecular motors. Here we demonstrate with quantitative measures of granule travel in the plane parallel to the plasma membrane that secretory granules change position within several hundred milliseconds of nicotinic agonist-induced fusion. Furthermore, just before fusion, granules frequently move to areas that they have rarely visited. The movement of granules to new areas is most evident for granules that fuse later during the stimulus. The movement may increase the probability of productive interactions of the granule with the plasma membrane or may reflect the pull of molecular interactions between the granule and the plasma membrane that are part of the fusion process. Thus, instead of being stably docked before exocytosis, granules undergo molecular-scale motions and travel immediately preceding the fusion event.
Epicutaneous antigen exposure induces a Th17 response that drives airway inflammation after inhalation challenge
Authors: He Rui , Oyoshi Michiko K. , Jin Haoli , Geha Raif S.
Published: September 2007

IL-17 has been implicated in a number of inflammatory diseases, but the conditions of antigen exposure that drive the generation of Th17 responses have not been well defined. Epicutaneous (EC) immunization of mice with ovalbumin (OVA), which causes allergic skin inflammation with many characteristics of the skin lesions of atopic dermatitis, was found to also drive IL-17 expression in the skin. EC, but not i.p., immunization of mice with OVA drove the generation of IL-17-producing T cells in draining lymph nodes and spleen and increased serum IL-17 levels. OVA inhalation by EC-sensitized mice induced IL-17 and CXCL2 expression and neutrophil influx in the lung along with bronchial hyperreactivity, which were reversed by IL-17 blockade. Dendritic cells trafficking from skin to lymph nodes expressed more IL-23 and induced more IL-17 secretion by naïve T cells than splenic dendritic cells. This was inhibited by neutralizing IL-23
in vitro
and by intradermal injection of anti-TGFβ neutralizing antibody
in vivo
. Our findings suggest that initial cutaneous exposure to antigens in patients with atopic dermatitis may selectively induce the production of IL-17, which, in turn, drives inflammation of their airways.
3D structure/function analysis of PilX reveals how minor pilins can modulate the virulence properties of type IV pili
Authors: Helaine Sophie , Dyer David H. , Nassif Xavier , Pelicic Vladimir , Forest Katrina T.
Published: September 2007

Type IV pili (Tfp) are widespread filamentous bacterial organelles that mediate multiple virulence-related phenotypes. They are composed mainly of pilin subunits, which are processed before filament assembly by dedicated prepilin peptidases. Other proteins processed by these peptidases, whose molecular nature and mode of action remain enigmatic, play critical roles in Tfp biology. We have performed a detailed structure/function analysis of one such protein, PilX from
Neisseria meningitidis
, which is crucial for formation of bacterial aggregates and adhesion to human cells. The x-ray crystal structure of PilX reveals the α/β roll fold shared by all pilins, and we show that this protein colocalizes with Tfp. These observations suggest that PilX is a minor, or low abundance, pilin that assembles within the filaments in a similar way to pilin. Deletion of a PilX distinctive structural element, which is predicted to be exposed on the filament surface, abolishes aggregation and adhesion. Our results support a model in which surface-exposed motifs in PilX subunits stabilize bacterial aggregates against the disruptive force of pilus retraction and illustrate how a minor pilus component can enhance the functional properties of pili of rather simple composition and structure.
Aquatic eutrophication promotes pathogenic infection in amphibians
Authors: Johnson Pieter T. J. , Chase Jonathan M. , Dosch Katherine L. , Hartson Richard B. , Gross Jackson A. , Larson Don J. , Sutherland Daniel R. , Carpenter Stephen R.
Published: September 2007

The widespread emergence of human and wildlife diseases has challenged ecologists to understand how large-scale agents of environmental change affect host–pathogen interactions. Accelerated eutrophication of aquatic ecosystems owing to nitrogen and phosphorus enrichment is a pervasive form of environmental change that has been implicated in the emergence of diseases through direct and indirect pathways. We provide experimental evidence linking eutrophication and disease in a multihost parasite system. The trematode parasite
Ribeiroia ondatrae
sequentially infects birds, snails, and amphibian larvae, frequently causing severe limb deformities and mortality. Eutrophication has been implicated in the emergence of this parasite, but definitive evidence, as well as a mechanistic understanding, have been lacking until now. We show that the effects of eutrophication cascade through the parasite life cycle to promote algal production, the density of snail hosts, and, ultimately, the intensity of infection in amphibians. Infection also negatively affected the survival of developing amphibians. Mechanistically, eutrophication promoted amphibian disease through two distinctive pathways: by increasing the density of infected snail hosts and by enhancing per-snail production of infectious parasites. Given forecasted increases in global eutrophication, amphibian extinctions, and similarities between
Ribeiroia
and important human and wildlife pathogens, our results have broad epidemiological and ecological significance.
Suppression of p53-dependent senescence by the JNK signal transduction pathway
Authors: Das Madhumita , Jiang Feng , Sluss Hayla K. , Zhang Chao , Shokat Kevan M. , Flavell Richard A. , Davis Roger J.
Published: September 2007

The JNK signaling pathway is implicated in the regulation of the AP1 transcription factor and cell proliferation. Here, we examine the role of JNK by using conditional and chemical genetic alleles of the ubiquitously expressed murine genes that encode the isoforms JNK1 and JNK2. Our analysis demonstrates that JNK is not essential for proliferation. However, JNK is required for expression of the cJun and JunD components of the AP1 transcription factor, and JNK-deficient cells exhibit early p53-dependent senescence. These data demonstrate that JNK can act as a negative regulator of the p53 tumor suppressor.
The yin and yang of intestinal epithelial cells in controlling dendritic cell function
Authors: Iliev Iliyan D. , Matteoli Gianluca , Rescigno Maria
Published: September 2007

Recent work suggests that dendritic cells (DCs) in mucosal tissues are “educated” by intestinal epithelial cells (IECs) to suppress inflammation and promote immunological tolerance. After attack by pathogenic microorganisms, however, “non-educated” DCs are recruited from nearby areas, such as the dome of Peyer's patches (PPs) and the blood, to initiate inflammation and the ensuing immune response to the invader. Differential epithelial cell (EC) responses to commensals and pathogens may control these two tolorogenic and immunogenic functions of DCs.
Endotoxemia and sepsis mortality reduction by non-anticoagulant–activated protein C
Authors: Kerschen Edward J. , Fernandez José A. , Cooley Brian C. , Yang Xia V. , Sood Rashmi , Mosnier Laurent O. , Castellino Francis J. , Mackman Nigel , Griffin John H. , Weiler Hartmut
Published: September 2007

Activated protein C (APC) reduces mortality of severe sepsis patients but increases the risk of serious bleeding. APC exerts anticoagulant activity by proteolysis of factors Va/VIIIa. APC also exerts antiinflammatory and antiapoptotic effects and stabilizes endothelial barrier function by APC-initiated cell signaling that requires two receptors, endothelial cell protein C receptor (EPCR) and protease-activated receptor 1 (PAR1). The relative importance of APC's various activities for efficacy in sepsis is unknown. We used protein engineering of mouse APC and genetically altered mice to clarify mechanisms for the efficacy of APC in mouse sepsis models. Mortality reduction in LPS-induced endotoxemia required the enzymatic active site of APC, EPCR, and PAR-1, highlighting a key role for APC's cytoprotective actions. A recombinant APC variant with normal signaling but <10% anticoagulant activity (5A-APC) was as effective as wild-type APC in reducing mortality after LPS challenge, and enhanced the survival of mice subjected to peritonitis induced by gram-positive or -negative bacteria or to polymicrobial peritoneal sepsis triggered by colon ascendens stent implantation. Thus, APC's efficacy in severe sepsis is predominantly based on EPCR- and PAR1-dependent cell signaling, and APC variants with normal cell signaling but reduced anticoagulant activities retain efficacy while reducing the risk of bleeding.