bluuebunny/crossref_metadata_2025 huggingface dataset:
The dual role of nitrogen as alloying and confining element in GaAs-based dilute nitride semiconductors
Authors: Porteanu H. E. , Loginenko O. , Koch F.
Published: February 2010

We examine transport and relaxation dynamics of optically excited electrons in GaAs-based heterostructure layers, involving dilute nitrides in percent-level concentration range. Such heterostructures contain materials with very different mobilities. Drift instead of Hall mobility is determined using a special technique. The value of the mobility of photogenerated electrons in a freestanding, 3% N InGaAsN layer, as part of a two-layer structure of 100 nm GaAs/2 μm nitride, is found to be of the order of 2 cm2/Vs, much lower than other values reported in the literature. The concomitant presence of carriers in the GaAs and nitride layers leads to formation of a barrier at the interface region that hinders electrons to enter in the nitride material. The dwell time of photoexcited electrons in GaAs interfacing the nitride layer is of the order of milliseconds, as seen by photoconductivity transients after pulsed optical excitation, much longer than the resulted time from optical experiments. Comparison of optical with transport properties reveals that the same centers involved in luminescence, that appear to be extended, are responsible also for hopping transport, where they appear as deep states. A theoretical explanation is given.
Bond-order potential for point and extended defect simulations in tungsten
Authors: Ahlgren T. , Heinola K. , Juslin N. , Kuronen A.
Published: February 2010

A reactive interatomic bond-order potential for bcc tungsten is presented. Special attention in the potential development was given for obtaining accurate formation and migration energies for point defects, making the potential useful in atomic scale simulations of point and extended defects. The potential was used to calculate binding energies and trapping distances for vacancies in vacancy clusters and the recombination radius for self-interstitial atom and monovacancy.
Enhancement of Co substitution induced by Eu codoping in ZnO-based diluted magnetic semiconducting thin films
Authors: Photongkam P. , Zhang Y. B. , Assadi M. H. N. , Li S. , Yu D. , Ionescu M. , Pan A. V.
Published: February 2010

To avoid the occurrence of doped magnetic ion clustering is a challenge in fabrication of diluted magnetic semiconductors (DMSs). In this work, we report the intrinsic ferromagnetic behavior in Co-doped ZnO DMSs induced by Eu codoping. Both structural parameters and magnetic properties demonstrate the existence of an interaction between Co and Eu ions. The observation of multiplet structures for the localized Co 3d states in x-ray absorption and x-ray magnetic circular dichroism characterization evidences that the codoped Eu plays an important role in facilitating the Co substitution of Zn, leading to intrinsic ferromagnetism.
AQUASOL: An efficient solver for the dipolar Poisson–Boltzmann–Langevin equation
Authors: Koehl Patrice , Delarue Marc
Published: February 2010

The Poisson–Boltzmann (PB) formalism is among the most popular approaches to modeling the solvation of molecules. It assumes a continuum model for water, leading to a dielectric permittivity that only depends on position in space. In contrast, the dipolar Poisson–Boltzmann–Langevin (DPBL) formalism represents the solvent as a collection of orientable dipoles with nonuniform concentration; this leads to a nonlinear permittivity function that depends both on the position and on the local electric field at that position. The differences in the assumptions underlying these two models lead to significant differences in the equations they generate. The PB equation is a second order, elliptic, nonlinear partial differential equation (PDE). Its response coefficients correspond to the dielectric permittivity and are therefore constant within each subdomain of the system considered (i.e., inside and outside of the molecules considered). While the DPBL equation is also a second order, elliptic, nonlinear PDE, its response coefficients are nonlinear functions of the electrostatic potential. Many solvers have been developed for the PB equation; to our knowledge, none of these can be directly applied to the DPBL equation. The methods they use may adapt to the difference; their implementations however are PBE specific. We adapted the PBE solver originally developed by Holst and Saied [J. Comput. Chem. 16, 337 (1995)] to the problem of solving the DPBL equation. This solver uses a truncated Newton method with a multigrid preconditioner. Numerical evidences suggest that it converges for the DPBL equation and that the convergence is superlinear. It is found however to be slow and greedy in memory requirement for problems commonly encountered in computational biology and computational chemistry. To circumvent these problems, we propose two variants, a quasi-Newton solver based on a simplified, inexact Jacobian and an iterative self-consistent solver that is based directly on the PBE solver. While both methods are not guaranteed to converge, numerical evidences suggest that they do and that their convergence is also superlinear. Both variants are significantly faster than the solver based on the exact Jacobian, with a much smaller memory footprint. All three methods have been implemented in a new code named AQUASOL, which is freely available.
Phase retrieval tomography in the presence of noise
Authors: Arhatari B. D. , Gates W. P. , Eshtiaghi N. , Peele A. G.
Published: February 2010

We describe the use of single-plane phase retrieval tomography using a laboratory-based x-ray source, under conditions where the retrieval is not formally valid, to present images of the internal structure of an Aerosil granule and a hydrated bentonite gel. The technique provides phase images for samples that interact weakly with the x-ray beam. As the method is less affected by noise than an alternative two-plane phase retrieval method that is otherwise formally valid, object structure can be observed that would not otherwise be seen. We demonstrate our results for phase imaging in tomographic measurements.
Group velocity dispersion and self phase modulation in silicon nitride waveguides
Authors: Tan D. T. H. , Ikeda K. , Sun P. C. , Fainman Y.
Published: February 2010

The group velocity dispersion (GVD) of silicon nitride waveguides, prepared using plasma enhanced chemical vapor deposition, is studied and characterized experimentally in support of nonlinear optics applications. We show that the dispersion may be engineered by varying the geometry of the waveguide and demonstrate measured anomalous GVD values as high as −0.57 ps2/m and normal GVD values as high as 0.86 ps2/m. We also experimentally demonstrate the absence of any observed nonlinear loss at the telecommunications wavelength at peak intensities of up to 12 GW/cm2. Spectral broadening due to self phase modulation in silicon nitride waveguides with a nonlinear parameter of 1.4 W−1/m is also demonstrated.
Central limit theorem for fluctuations of linear eigenvalue statistics of large random graphs
Authors: Shcherbina Mariya , Tirozzi Brunello
Published: February 2010

We consider the adjacency matrix A of a large random graph and study fluctuations of the function fn(z,u)=(1/n)∑k=1nexp{−uGkk(z)} with G(z)=(z−iA)−1. We prove that the moments of fluctuations normalized by n−1/2 in the limit n→∞ satisfy the Wick relations for the Gaussian random variables. This allows us to prove central limit theorem for Tr G(z) and then extend the result on the linear eigenvalue statistics Tr φ(A) of any function φ:R→R which increases, together with its first two derivatives, at infinity not faster than an exponential.
Atomic scale analysis of self assembled GaAs/AlGaAs quantum dots grown by droplet epitaxy
Authors: Keizer J. G. , Bocquel J. , Koenraad P. M. , Mano T. , Noda T. , Sakoda K.
Published: February 2010

In this letter we have performed a structural analysis at the atomic scale of GaAs/AlGaAs quantum dots grown by droplet epitaxy. The shape, composition, and strain of the quantum dots and the AlGaAs matrix are investigated. We show that the GaAs quantum dots have a Gaussian shape and that minor intermixing of Al with the GaAs quantum dot takes place. A wetting layer with a thickness of less than one bilayer was observed.
Enhanced ultraviolet electroluminescence from ZnO nanowires in TiO2/ZnO coaxial nanowires/poly(3,4-ethylenedioxythiophene)-poly(styrene-sulfonate) heterojunction
Authors: Lee Chun-Yu , Wang Jen-Yi , Chou Yi , Liu Meng–Yueh , Su Wei-Fang , Chen Yang-Fang , Lin Ching-Fuh
Published: February 2010

The ultraviolet (UV) electroluminescence (EL) from the TiO2/ZnO coaxial nanowires (NWs)/poly(3,4-ethylenedioxythiophene)-poly(styrene-sulfonate) inorganic/organic heterostructure devices is greatly enhanced and the defect emission is significantly suppressed compared with the uncoated ZnO NW device at room temperature. The origins of the great changes in EL of ZnO NW devices are attributed to the surface modification of the sputtered TiO2 coating and the reduction in the pinhole traps on the surface of ZnO NWs. It is found that for the optimized device, the EL intensity ratio between the band gap and defect emission can be greatly enhanced by up to about 250 times its prior level. Such ZnO NW devices with enhanced UV emission have potential applications in the highly efficient solid state emitters.
Controllable spin-polarized electrical transport in wide-band-gap oxide ferromagnetic semiconductors
Authors: Tian Y. F. , Yan Shi-shen , Zhao M. W. , Dai Y. Y. , Zhang Y. P. , Qiao R. M. , Hu S. J. , Chen Y. X. , Liu G. L. , Mei L. M. , Qiang Y. , Jiao J.
Published: February 2010

A family of wide-band-gap ternary oxide ferromagnetic semiconductor films with high transition metal concentration was prepared. The resistivity of these films can be changed up to four orders of magnitude by varying the composition or the concentration of the oxygen vacancies. Moreover, all these films show common features in electrical transport, i.e., Mott variable range hopping (VRH) in the lower resistivity range, Efros VRH in the middle resistivity range, and “hard gap” resistance in the higher resistivity range. The above phenomena are well understood by considering the relative magnitude of three characterization lengths, i.e., Coulomb screening length, localization length of the carriers, and optimal hopping distance. Furthermore, spin polarization ratio of these magnetic semiconductors was obtained by fitting the experimental results of electrical transport. Therefore, the wide gap oxide ferromagnetic semiconductors with controllable spin-polarized electrical transport are expected to have application in spintronics devices as a spin injection source.
Theoretical and experimental investigation of optically driven nanoelectromechanical oscillators
Authors: Ilic B. , Krylov S. , Craighead H. G.
Published: February 2010

The actuation of biologically functional micro- and nanomechanical structures using optical excitation is an emerging arena of research that couples the fields of optics, fluidics, electronics, and mechanics with potential for generating novel chemical and biological sensors. In our work, we fabricated nanomechanical structures from 200 and 250 nm thick silicon nitride and single crystal silicon layers with varying lengths and widths ranging from 4 to 12 μm and 200 nm to 1 μm, respectively. Using a modulated laser beam focused onto the device layer in close proximity to the clamped end of a cantilever beam, we concentrate and guide the impinging thermal energy along the device layer. Cantilever beams coupled to chains of thermally isolated links were used to experimentally investigate energy transport mechanisms in nanostructures. The nature of the excitation was studied through steady-periodic axisymmetric thermal analysis by considering a multilayered structure heated using a modulated laser source. Results were verified by finite element analysis, which was additionally implemented for the solution of steady-periodic and transient thermal, as well as steady thermoelastic problems. These theoretical investigations, coupled with our experimental results, reveal that the complex dynamics underpinning optical excitation mechanisms consists of two disparate spatial regimes. When the excitation source is focused in close proximity to the structure the response is primarily thermal. We show that as the source is placed farther from the clamped end of the structure, the thermal response progressively fades out, indicating the possibility of mechanical wave propagation. Understanding the excitation mechanisms may be useful for applications including compact integration of nanophotonic elements with functionalized nanomechanical sensors for ultrasensitive biochemical analysis.
Self-assembled templating for the growth of molecular nanodots
Authors: Yokoyama Takashi
Published: February 2010

A checkerboard pattern of α-sexithiophene (α-6T) with an approximate lattice size of 2.6×3.3 nm2 has been achieved on a Ag(110) surface at monolayer coverage, which is formed through a lateral ordering of two oriented molecules and vacancy defects. We find that this self-assembled pattern provides a template structure for the formation of molecular nanodots and nanocolumns. Second and third-layer islands of α-6T are formed within the checkerboard lattice, leading to a uniform molecular nanodot array, and a nanosized columnar structure is expected if growth is continued into the multilayer regime.
On the linear response and scattering of an interacting molecule-metal system
Authors: Masiello David J. , Schatz George C.
Published: February 2010

A many-body Green’s function approach to the microscopic theory of plasmon-enhanced spectroscopy is presented within the context of localized surface-plasmon resonance spectroscopy and applied to investigate the coupling between quantum-molecular and classical-plasmonic resonances in monolayer-coated silver nanoparticles. Electronic propagators or Green’s functions, accounting for the repeated polarization interaction between a single molecule and its image in a nearby nanoscale metal, are explicitly computed and used to construct the linear-response properties of the combined molecule-metal system to an external electromagnetic perturbation. Shifting and finite lifetime of states appear rigorously and automatically within our approach and reveal an intricate coupling between molecule and metal not fully described by previous theories. Self-consistent incorporation of this quantum-molecular response into the continuum-electromagnetic scattering of the molecule-metal target is exploited to compute the localized surface-plasmon resonance wavelength shift with respect to the bare metal from first principles.
Perpendicular FePt-based exchange-coupled composite media
Authors: Makarov D. , Lee J. , Brombacher C. , Schubert C. , Fuger M. , Suess D. , Fidler J. , Albrecht M.
Published: February 2010

Exchange-coupled composite media were realized by combining perpendicular hard magnetic FePtCu alloy films with perpendicular Co/Pt multilayers which are magnetically softer. We demonstrate that the switching field of the hard layer can be efficiently altered by modifying the material properties of the soft layer by varying the number of Co/Pt bilayers. Moreover, the possibility of effectively tuning the interlayer exchange coupling using rapid thermal annealing was shown. These studies were supported by theoretical modeling revealing the relevant factors to reduce the switching field of the hard layer which are important for future media design.
Temperature-dependent shear band dynamics in a Zr-based bulk metallic glass
Authors: Klaumünzer David , Maaß Robert , Torre Florian H. Dalla , Löffler Jörg F.
Published: February 2010

Flow serrations recorded during inhomogeneous deformation of Zr52.5Ti5Cu17.9Ni14.6Al10 (Vit105) were studied during compression testing at temperatures between −40 and 60 °C. The shear band velocities determined exhibit a pronounced temperature dependence covering nearly two orders of magnitude. The velocities follow an Arrhenius-type behavior with an associated activation energy of 0.3±0.05 eV. The results demonstrate a thermally activated mechanism of shear band propagation, which is similar to the behavior of other, nonmetallic amorphous materials.
Losses in coplanar waveguide resonators at millikelvin temperatures
Authors: Macha P. , van der Ploeg S. H. W. , Oelsner G. , Il’ichev E. , Meyer H.-G. , Wünsch S. , Siegel M.
Published: February 2010

We study the loss rate for a set of λ/2 coplanar waveguide resonators at millikelvin temperatures (20–900 mK) and different applied powers (3⋅10−19–10−12 W). The loss rate becomes power independent below a critical power. For a fixed power, the loss rate increases significantly with decreasing temperature. We show that this behavior can be caused by two-level systems in the surrounding dielectric materials. Interestingly, the influence of the two-level systems is of the same order of magnitude for the different material combinations. That leads to the assumption that the nature of these two-level systems is material independent.
Crystallitic orientation effects on charge transport in polythiophene thin-film transistors
Authors: Zhou Liping , Wang Xue-Feng , Han Qin , Wu Jian-Chun , Li Zhen-Ya
Published: February 2010

We simulate charge transport through polymer grain boundaries under the buried critical interface of polymer and dielectric in polythiophene thin-film transistors and find the recently observed enhancement of electronic conduction can be a result of optimized crystallitic orientation. The simulation is based on a first-principle description of the system with transport properties evaluated by nonequilibrium Green's function method. Highly oriented crystal is assumed inside each grain and four most probable configurations of crystallitic orientation for grain boundary are considered. The calculation confirms that the electronic conductance can differ by five orders in magnitude for different conformations.
Mobility analysis of highly conducting thin films: Application to ZnO
Authors: Look D. C. , Leedy K. D. , Tomich D. H. , Bayraktaroglu B.
Published: February 2010

Hall-effect measurements have been performed on a series of highly conductive thin films of Ga-doped ZnO grown by pulsed laser deposition and annealed in a forming-gas atmosphere (5% H2 in Ar). The mobility as a function of thickness d is analyzed by a simple formula involving only ionized-impurity and boundary scattering and having a single fitting parameter, the acceptor/donor concentration ratio K=NA/ND. For samples with d=3–100 nm, Kavg=0.41, giving ND=4.7×1020 and NA=1.9×1020 cm−3. Thicker samples require a two-layer formulation due to inhomogeneous annealing.
Statistical composition-structure-property correlation and glass-forming ability based on the full icosahedra in Cu–Zr metallic glasses
Authors: Sha Z. D. , Feng Y. P. , Li Y.
Published: February 2010

Using the large-scale atomic/molecular massively parallel simulator, fraction of the Cu-centered ⟨0,0,12,0⟩ full icosahedra (fico) is obtained from a statistical analysis over a broad compositional range with high resolution in the Cu–Zr binary system. Weak but significant peaks are observed at certain compositions which coincide with good glass formers. This correlation implies that the change in fico is a fundamental structural factor in determining the ease of glass formation. In this regard, fico can be an indicator of glass-forming ability. Our work provides further understanding on the atomic structure of the Cu–Zr system and its effect on glass formation.
Ultrafast terahertz photoconductivity in nanocrystalline mesoporous TiO2 films
Authors: Němec H. , Kužel P. , Kadlec F. , Fattakhova-Rohlfing D. , Szeifert J. , Bein T. , Kalousek V. , Rathouský J.
Published: February 2010

Terahertz time-resolved spectroscopy is used to investigate the transport of photoexcited electrons in nanocrystalline mesoporous TiO2 films prepared by the recently proposed “brick and mortar” technology [Szeifert et al.Chem. Mater. 21, 1260 (2009)] with a variable fraction of nanocrystalline titania “bricks” and amorphous titania “mortar.” Both long- and short-range conductivity is significantly enhanced upon calcination. After an ultrafast (subpicosecond) regime where the intrananograin conductivity dominates, the electron conductivity becomes limited by the interaction of electrons with the amorphous mortar. Comparison of the experimental results with Monte Carlo simulations of the electron motion allows us to determine the crystalline grain size after calcination and the yield of mobile photocarriers.
Assessment of an analytical density matrix derived from a modified Colle–Salvetti approach to the electron gas
Authors: Ragot Sébastien
Published: February 2010

The Ragot–Cortona model of local correlation energy [S. Ragot and P. Cortona, J. Chem. Phys. 121, 7671 (2004)] revisits the initial approach of Colle and Salvetti [Theor. Chim. Acta 37, 329 (1975)] in order to reinstate the kinetic contribution Tc to the total correlation energy Ec. In this work, the one-electron reduced density matrix underlying the amended model is fully derived in closed form. By construction, the said density matrix is parameter-free but not N-representable, owing to approximations used in the Ragot–Cortona approach. However, the resulting density matrix is shown to have formally correct short- and long-range expansions. Furthermore, its momentum-space counterpart qualitatively agrees with known parametrized momentum distributions except at small momenta, where the disagreement reflects the nonrepresentability of the model and restricts to a small fraction of the slowest electrons only.
Effect of time since burn on soil seedbanks in the jarrah forest of Western Australia
Authors: Koch John M. , Ruschmann Alex M. , Morald Tim K.
Published: February 2010

Bauxite is mined in the jarrah (Eucalyptus marginata Sm.) forest of south-western Australia and 700–800 ha each year are rehabilitated by mining companies. As well as broadcasting seeds and planting, the mine restoration relies heavily on the natural soil seedbank as a means of reinstating plant diversity after mining. The natural soil seedbank is a large but highly variable resource, both spatially and temporally. In the present study, we used 32 sites paired across burn boundaries to determine changes in soil seedbanks due to time since burn. At each site, we took one hundred 100-cm2 soil samples down to 5-cm depth and recorded germinable seeds. The mean total seedbank over all sites was 472 seeds m–2 (90–1210 seeds m–2). Five months after a spring burn, there was a significant decrease in the seedbank of legumes, compared with unburnt sites, probably due to germination in spring immediately after burning. Non-legumes (mostly non-heat-responsive species) did not show this decrease. One year after burning, there was a significant reduction in the total seedbank, presumably due to germination of most species in the winter following the burn. Legumes and non-legumes both showed this decrease. There was a recovery of the soil seedbank by 3 years after burning. This recovery was associated with higher densities of species from the families Apiaceae, Rhamnaceae (Trymalium ledifolium Fenzl), Stylidiaceae, Rutaceae, Centrolepidaceae and Sterculiaceae (Lasiopetalum floribundum Benth.). These families represent annuals, herbaceous species and small perennial shrubs. The recovery was likely due to vigorous flowering, and seed set by seedlings and sometimes resprouts following the burn. Once recovered, the soil seedbank stayed reasonably consistent up to 22 years after burning. Soils stripped 1 year after burning may contribute less plant density and diversity to rehabilitated areas. There is no evidence that the soil seedbank significantly decreases in the longer term with increasing time since burning up to 22 years. The community composition of the soil seedbank was strongly affected by geographical location, with sites closer to each other having similar composition. Only sites 1-year-since burn showed changes in the community composition due to burning.
Population ecology and genetics of the vulnerable Acacia attenuata (Mimosaceae) and their significance for its conservation, recovery and translocation
Authors: Brownlie Heather , Playford Julia , Wallace Helen , Shapcott Alison
Published: February 2010

Acacia attenuata Maiden and Blakely, is a vulnerable shrub, endemic to south-east Queensland, Australia. The population ecology and genetics of the species were examined throughout its range to assist with conservation and recovery of the species. South-east Queensland is experiencing massive population expansion and the associated housing and infrastructure development is having an impact on the remnant vegetation in the region. Population sizes differed significantly (P < 0.05) and were smaller in the southern urbanised parts of the species distribution. Genetic diversity of A. attenuata was high in comparison to other Acacia species. Genetic diversity was not significantly correlated with population size or isolation. There was a high degree of genetic similarity among populations (FST = 0.101). Populations were effectively inbred (F = 0.482); however, inbreeding was not correlated with population size, density, isolation or reproductive activity. Uniform high levels of genetic diversity and low population differentiation suggest that A. attenuata once had a more continuous distribution. A population that was due to be translocated because of a development decision was also assessed as part of the research. The population at the development site (AA14 – Bundilla) was the largest and one of the most genetically variable sites, thus the genetic diversity of the population needs to be conserved within the translocation. The translocation process is reported here and occurred based on the information on genetics and ecology provided by this study. Population density and the proportion of seedlings and juveniles were significantly negatively correlated with time since fire. Fire regimes of 5–10 years are optimal for A. attenuata population regeneration and persistence, thus active fire management will be required for both the translocated population and for other populations within the urban and peri-urban areas, where competing demands make fire management controversial and difficult.
Tolerance of Sesbania virgata plants to flooding
Authors: Zanandrea Ilisandra , Alves José D. , Deuner Sidnei , Goulart Patrícia de F. P. , Henrique Paôla de C. , Silveira Neidiquele M.
Published: February 2010

Sesbania virgata (Cav.) Pers. is a bush, pioneer and occurs naturally in Brazil. It belongs to the Fabaceae family and it is indicated for recovery of degraded areas because of its rusticity and capacity to tolerate flooding. The present research was carried out to investigate the ability of S. virgata plants to adapt to flooding conditions. Plants containing six expanded leaves were placed in masonry tanks and were subjected to the following conditions: control (well watered), soil-waterlogging (water to the setup level of 1 cm above the soil surface – roots and parts of the stems flooded) and complete submergence (whole plant flooded). The evaluations were conducted on the day of the stress induction and after 7, 14, 21, 28, 35, 42, 49 and 56 days of the treatment. After 15 days of return to normoxic environment, plant survival was assessed. Growth (height, dry mass of shoots and roots), vigour, carbohydrate content and the activity of enzymes involved in anaerobic metabolism (lactate dehydrogenase, pyruvate decarboxylase and alcohol dehydrogenase) were also evaluated. Our results suggested that sesbania plants are tolerant to flooding, because they can survive being submerged for 56 days. The reasons for this tolerance include the accumulation and use of carbohydrates in the leaves and roots, maintenance of growth and the activation of anaerobic metabolism, particularly in steps catalysed by the enzymes pyruvate decarboxylase and alcohol dehydrogenase.
Corrigendum to: Fertiliser N and P applications on two Vertosols in north-eastern Australia. 2. Grain P concentration and P removal in grain from two long-term experiments
Authors: Lester David W. , Birch Colin J. , Dowling Chris W.
Published: February 2010

Within north-eastern Australia's grain-production region there are few reports outlining nitrogen (N) and phosphorus (P) fertiliser effects on grain P concentration and P removal in grain. Two long-term N�נP fertiliser experiments with different cultivation durations were conducted, one at ?Colonsay' on the Darling Downs in southern Queensland (commencing 1985 after 40 years of cultivation), and the other at ?Myling' on the north-west plains of New South Wales (commencing 1996 after 9 years of cultivation). Applications of N and P fertiliser independently influenced both grain P concentration and P removal for a range of summer and winter cereal and legume crops. Generally, if N fertiliser application increased grain yield, the grain P concentration decreased as grain yield increased; however, if grain yield did not respond to N fertiliser, grain P concentration was unaffected. P fertiliser applications typically increased grain P concentration. Wheat and barley grain P concentrations were generally higher in this subtropical region than reported values from temperate regions in Australia. Grain sorghum values were similar to those from subtropical areas overseas, but were greater than reported values from more tropical production zones. Mungbean and chickpea grain P concentrations were consistent with other reported values. Experimental results indicated grain P concentrations for estimating grain P removal in the northern grains region of 3400�mg/kg for sorghum, 3500�mg/kg for wheat and barley, and 4000–4500�mg/kg for mungbean.
At both sites, grain P removal was greater with summer and winter cereals than with legume crops. Larger grain yields with N fertiliser application had the largest influence on grain P removal at the Colonsay site, with an additional 23.3�kg�P/ha removed from plots with 80�kg�N/ha applied compared with nil N over 5 analysed crops from 1998 to 2003. Grain P removal was 20.9, 17.1, and 19.7�kg�P/ha in the 3 sorghum crops at this site in this period. Thus, application of P at 10�kg�P/ha.crop for this 5-crop study period did not replace P removed. In the predominantly winter-cropped Myling experiment with a shorter duration of cultivation and smaller N fertiliser response, cumulative removal was more influenced by P fertiliser, with 10�kg fertiliser P/ha.crop generally sufficient to provide replacement P. These results support findings of negative P balances recently reported for grain production in this region and suggest a need for further investigation into the implications of a continuing negative P balance on the sustainability of grain production.
An epidemiological model for externally acquired vector-borne viruses applied to Beet western yellows virus in Brassica napus crops in a Mediterranean-type environment
Authors: Maling T. , Diggle A. J. , Thackray D. J. , Siddique K. H. M. , Jones R. A. C.
Published: February 2010

A hybrid mechanistic/statistical model developed previously to predict vector activity and epidemics of vector-borne viruses was modified to simulate virus epidemics in the Beet western yellows virus (BWYV) – Brassica napus pathosystem. BWYV, which is persistently aphid-borne, spreads to B. napus crops from external sources and causes substantial yield losses when there is widespread infection of young plants. Risk that such losses may occur depends on the magnitude and availability of viral inoculum in the external source, the amount of biomass available to support aphid vectors, its duration before crop emergence, and the time of arrival of vector aphids in the crop. The model uses daily rainfall, temperature, and evaporation data from over 450 sites in the grainbelt of south-western Australia to track biomass levels throughout the growing season. This information is then used to simulate aphid vector populations and virus incidence, initially in the external source environment, then in the crop, and ultimately to provide risk forecasts. The model predicted BWYV spread successfully for 10 of 12 different datasets from 3 years of field observations on B. napus blocks at 4 sites representing different rainfall and geographic zones of the grainbelt. Sensitivity analysis was used to determine the relative importance of the main parameters that describe the pathosystem and to predict which control measures are likely to be useful. An analysis of timing of predictions v. their accuracy was also done to establish optimum timing of forecasts for BWYV epidemics in B. napus crops.
QTLs and their interaction determining different heading dates of barley in Australia and China
Authors: Ren Xifeng , Li Chengdao , Boyd W. J. R. , Westcott Sharon , Grime C. R. , Sun Dongfa , Lance Reg
Published: February 2010

Heading date is a major determinant of the regional and seasonal adaptation of barley varieties. The dogma is that introduced germplasm is more likely to be adapted if it is derived from a similar latitude. However, barley germplasm introduced from similar latitudes of South-East Asia is extremely early heading in the Australian environments and vice versa. A doubled-haploid population from a cross of an Australian barley Galleon and a Japanese barley Haruna Nijo was evaluated for heading date in Australia (Perth, 31°56′S) and China (Wuhan, 30°33′N) under normal autumn sowing, late sowing in the field, and extended-light glasshouse conditions. One major QTL was identified on chromosome 5H under the three conditions in China. The single QTL accounted for up to 50% of phenotypic variation for heading date. The Australian variety contributed to late heading date. Two QTLs on chromosomes 4H and 5H were detected for controlling heading date in Australia. The QTL/QTL interaction contributed up to 35.8% of phenotypic variation for heading date in Australia, which is the major reason for the extremely early heading date of the Japanese variety in the Australian environment. The chromosome 5H QTL was detected at the same chromosomal location when the population was grown in either China or Australia. In both environments the Australian variety contributed to the late heading date. Selection against the Japanese alleles of chromosomes 4H and 5H QTLs could eliminate the extremely early genotype in Australia and selection against the Australian allele of chromosome 5H QTL could eliminate the extremely late genotype in China when Australian and Japanese germplasms are used in the breeding programs.
The response of rate and duration of grain filling to long-term selection for yield in Italian durum wheats
Authors: Motzo Rosella , Giunta Francesco , Pruneddu Giovanni
Published: February 2010

Genetic advance in durum wheat (Triticum turgidum subsp. durum) grain yield in Italy has been achieved by bringing forward flowering time, achieving a larger number of grains per unit area, and altering the pattern of senescence. The performance, in the absence of any moisture stress, of a set of 6 Italian durum wheat cultivars released over the past 100 years was compared under 4 environments and 2 nitrogen rates, to ascertain whether the changes brought about by selection for yield have also indirectly affected the rate and duration of grain filling. Grain filling lasted 35–36 days in all cultivars except ‘Ichnusa’ (39 days), although modern cultivars flowered earlier than older ones. The lack of any breeding effect on grain-filling duration also meant that the later old cultivars were not negatively affected by the higher ambient temperatures during their grain filling. The maximum rate of grain filling ranged from 2.4 to 3.3 mg/day and showed a highly significant negative correlation with the year of cultivar release (r = –0.91*). The variation in grain weight, significant but not correlated with the year of release, was associated with the rate of grain filling, which was in turn related to the grain number per unit area. A compensating variability still exists among modern Italian cultivars in both grain number and grain-filling rate, which demonstrates that durum wheat grain yield can be increased while also preserving high grain weights.
Field studies of the effects of pre-sowing weed control and time of sowing on tropical perennial grass establishment, North-West Slopes, New South Wales
Authors: Lodge G. M. , Brennan M. A. , Harden S.
Published: February 2010

Two separate experiments on the North-West Slopes of New South Wales investigated: (1) the effects of differing lengths of pre-sowing weed control (2 years, 1 year, and 3–4 months in the spring immediately before sowing) on the soil seed density of liverseed grass (Urochloa panicoides) from November 2005 to November 2007 and its seedling density at establishment (December 2007), as well as on subsequent herbage mass and plant frequency of this species and Panicum coloratum var. makarikariense cv. Bambatsi (Expt 1); and (2) the effects of cultivar, time of sowing (November 2006, January 2007, and March 2007), and defoliation in the autumn after sowing, on the over-wintering ability of 5 tropical perennial grasses (Expt 2). The cultivars sown in Expt 2 were Bambatsi, Dichanthium aristatum cv. Floren, Chloris gayana cv. Katambora, Digitaria eriantha var. eriantha cv. Premier, and Bothriochloa bladhii var. glabra cv. Swann.
At sowing (November 2007), liverseed grass seed and seedling densities in Expt 1 were lowest (P < 0.05) in the 2-year pre-sowing weed control treatment (15 and 13/m2, respectively), and the subsequent herbage mass of Bambatsi (January and October 2008) was highest (P < 0.05) in this treatment. In Expt 2, 59 frosts occurred in 2007, and Floren, Bambatsi, and Swann sown in March of that year over-wintered poorly and had lower (P < 0.05) herbage mass and plant frequency in the following spring compared with the other sowing times. These differences were also evident in autumn and spring 2008, up to 23 months after sowing.
Genetics of late maturity α-amylase in a doubled haploid wheat population
Authors: Tan M. K. , Verbyla A. P. , Cullis B. R. , Martin P. , Milgate A. W. , Oliver J. R.
Published: February 2010

Late maturity α-amylase (LMA) in wheat is a defect where high-isoelectric point (pI) α-amylase accumulates in the ripening grain. Wheat genotypes vary in expression from zero to high levels of α-amylase, the latter with detrimental consequences on their use for value-added end products. Expression in each genotype is characterised by varying numbers of grains affected and different levels in each grain. Analysis of a doubled haploid (DH) population (188 lines) from WW1842 × Whistler has identified significant QTL on chromosomes 2DL, 3A, 3B, 3D, 4B, 4D, 5DS and 5BL. The 4B LMA allele (P < 0.0001) from Whistler is closely linked to the QTL for the ‘tall’ allele (P < 0.0001) of the Rht-B1 gene. The 4D LMA QTL (P < 0.0001) in WW1842 co-locates with the QTL for the ‘tall’ allele (P < 0.0001) of the Rht-D1 gene. This study has shown for the first time that a DH cross between two semi-dwarf cultivars with low or no LMA produces ~25% of progeny lines of the ‘tall’ genotypes with a high frequency of LMA. This is attributed to the large additive positive effects from the combination of one recessive ‘tall’ Rht-B1 gene and one recessive ‘tall’ Rht-D1 gene. High-yielding semi-dwarf genotypes with different combinations of Rht-B1 and Rht-D1 alleles which have very low or non-existent LMA expression (e.g. WW1842 and Whistler) may meet industry criteria for registration as commercial wheat varieties. However, when they are used as breeding lines, the cross produces some progeny genotypes with severe levels of LMA. These LMA genotypes comprise the gibberellic acid-sensitive ‘tall’ progenies and a very small proportion of semi-dwarfs. Thus, it is of paramount importance to screen the defect in wheat breeding programs. The suite of QTL identified for LMA will enable the use of marker assisted selection in the pyramiding of the beneficial QTL to maximise yield and minimise (or eliminate) LMA in semi-dwarf genotypes.
Sucrose accumulation in sugarcane is influenced by temperature and genotype through the carbon source - sink balance
Authors: Inman-Bamber N. G. , Bonnett G. D. , Spillman M. F. , Hewitt M. H. , Glassop D.
Published: February 2010

While substantial effort has been expended on molecular techniques in an attempt to break through the apparent ceiling for sucrose content (SC) in sugarcane stalks, molecular processes and genetics limiting sucrose accumulation remain unclear. Our own studies indicate that limiting expansive growth with water stress will enhance sucrose accumulation in both low- and high-sucrose clones. Sucrose accumulation was largely explained (72%) by an equation with terms for photosynthesis, plant extension rate (PER), and plant number. New research was conducted to determine if this simple model stands when using temperature rather than water stress to perturb the source–sink balance. We also applied a thinning treatment to test the proposal implicit in this equation that SC will increase if competition between plants for photo-assimilate is reduced.
Four clones from a segregating population representing extremes in SC were planted in pots and subjected to warm and cool temperature regimes in a glasshouse facility. A thinning treatment was imposed on half the pots by removing all but 6 shoots per pot.
Temperature as a means of reducing sink strength seemed initially to be more successful than water regime because PER was 43% lower in the cool than in the hot regime while photosynthesis was only 14% less. PER was a good indicator of dry matter allocation to expansive growth, limited by water stress but not by temperature, because stalks tended to thicken in low temperature. Thinning had little effect on any of the attributes measured. Nevertheless the clonal variation in plant numbers and the response of PER to temperature helped to explain at least 69% of the variation in sucrose accumulation observed in this experiment. Thus the earlier model for sucrose accumulation appeared to be valid for the effect on sucrose accumulation of both temperature and water stress on the source–sink balance. The next step is to include internodes in models of assimilate partitioning to help understand the limiting steps in sucrose accumulation from the basics of source–sink dynamics.
Alternative mating tactics in the New Zealand fur seal (Arctocephalus forsteri): when non-territorial males are successful too
Authors: Caudron A. K. , Negro S. S. , Fowler M. , Boren L. , Poncin P. , Robertson B. C. , Gemmell N. J.
Published: February 2010

In polygynous mammals, the status of many males does not allow them to have a high social rank and theory predicts selection for alternative mating tactics. Alternative tactics were suggested to explain discrepancies between mating and paternity successes in several pinniped species. However, information on alternative tactics in fur seals is limited. Here, we focus on the polygynous New Zealand fur seal, Arctocephalus forsteri, predicting that competition for females is likely to cause a diversification of male mating tactics and that non-territorial tactics can yield reproductive success. We describe the behaviour of 38 males in a medium to large colony. Paternity success was assessed using CERVUS and PASOS, from a pool of 82 pups sampled at the study site and at neighbouring breeding areas. To see whether size is correlated with mating tactic, the length of 17 males was estimated using photogrammetry. Cluster analysis identified three male behavioural profiles: one corresponding to large territorial males and two illustrating alternative tactics employed by smaller non-territorial males. Of the 13 pups born at the study site that were assigned a father, eight were sired by three territorial males and five were sired by non-territorial males. Our study highlights that holding a territory is not a necessary condition for reproductive success in all otariids.
Chemical cues and group association preferences in a subsocial cockroach, Panesthia australis
Authors: Billingham Zacariah D. , Chapple David G. , Sunnucks Paul , Wong Bob B. M.
Published: February 2010

An ability to recognise and discriminate between group and non-group members is essential for most group-living species. Several different sensory modalities may be utilised for social recognition, the most notable of which is olfaction. Among insects, members of the order Blattodea (cockroaches, termites) exhibit a diverse range of social systems and provide an excellent model for examining the role of chemical communication in group discrimination. We experimentally tested the importance of chemical cues in the association preferences of the subsocial Australian wood-boring cockroach, Panesthia australis. Using a series of dichotomous choice trials, we found that individuals preferred conspecific odour cues over those of an unscented peatmoss control. We then gave cockroaches a choice between the odour cues of cockroaches from different logs, and found that they did not exhibit a preference for the cues of individuals from their own log versus those from different logs within the same locality. However, cockroaches exhibited a strong preference for cues taken from individuals from a geographically distant population. Our findings suggest that P. australis engages in group discrimination, and that patterns of association may reflect an underlying preference for unfamiliar and/or genetically dissimilar individuals in a species encumbered by restricted gene flow.
Parasites of Rattus colletti (Rodentia:Muridae) from the Adelaide River floodplain, Northern Territory, and comparison with assemblages in other Rattus species
Authors: Mulder E. , Smales L. R.
Published: February 2010

This study documents the parasite assemblage of Rattus colletti (Thomas, 1904) from the Adelaide River flood plain, Northern Territory, Australia. In total, six species of helminth (comprising two cestodes, one trematode and three nematodes), and four species of arthropod (comprising one tick, one mite, one flea (identified to family level) and one louse (identified to generic level)) were found. In spite of the hosts being present in high numbers the helminth assemblage was depauperate, characterised by low prevalence and abundance, both being higher in wet seasons. More helminths were found in larger animals. The most prevalent helminth was from the Trichostrongylina, Nippostrongylus typicus (Mawson, 1961). The assemblage was characterised as having two heirloom species (N. typicus and Hymenolepis diminuta (Rudolphi, 1819)), a host capture (Raillietina celebensis (Janicki, 1902) and a cosmopolitan species (Mastophorus muris (Gmelin, 1790)) as well as occasional infections. When compared with the helminths from a single population of Rattus sordidus (Gould, 1858) a similar number of species were found, three species being in common, and both were depauperate when compared with the more extensively surveyed faunas of Rattus fuscipes (Waterhouse, 1839) and Rattus leucopus (Gray, 1858).