bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical characterization of Au-doped rhenium diselenide single crystals
Authors: Dumcenco D. , Huang Y. S. , Liang C. H. , Tiong K. K.
Published: September 2008

In this paper, the optical properties of Au-doped rhenium diselenide (ReSe2:Au) single crystals have been reported. The doping effects of the material were characterized by polarization-dependent transmittance, piezoreflectance (PzR), and photoreflectance (PR) measurements in the temperature range of 15–300 K. The indirect energy gap of ReSe2:Au shows a slight redshift with respect to the undoped sample. The low temperature PzR and PR spectra reveal an E1ex feature at E∥b polarization as well as two features, E2ex and E3ex, at E⊥b polarization. The angular dependence of the excitonic feature amplitudes agrees well with Malus’ law. In comparison with the undoped ReSe2, the excitonic transition energies remain practically unchanged, while the broadening parameter of the excitonic transition features slightly increases due to impurity scattering. In addition, the parameters that describe the temperature variations of the band-edge excitonic transitions were evaluated and discussed.
Electronic state modification in laser deposited amorphous carbon films by the inclusion of nitrogen
Authors: Miyajima Y. , Adamopoulos G. , Henley S. J. , Stolojan V. , Tison Y. , Garcia-Caurel E. , Drévillon B. , Shannon J. M. , Silva S. R. P.
Published: September 2008

In this study, we investigate the effect of the inclusion of nitrogen in amorphous carbon thin films deposited by pulsed laser deposition, which results in stress induced modifications to the band structure and the concomitant changes to the electronic transport properties. The microstructural changes due to nitrogen incorporation were examined using electron energy-loss spectroscopy and Raman scattering. The band structure was investigated using spectroscopic ellipsometry data in the range of 1.5–5 eV, which was fitted to the Tauc Lorentz model parametrization and optical transmittance measurements. The dielectric constant evaluated using optical techniques was compared to that obtained with electrical measurements, assuming a Poole-Frenkel type conduction process based on the best fits to data. The electrical conduction mechanism is discussed for both low and high electric fields, in the context of the shape of the band density of states. By relating a wide range of measurement techniques, a detailed relationship between the microstructure, and the optical and the electrical structures of a-CNx films is obtained. From these measurements, it was found that, primarily, the change in density of the film, with increasing nitrogen pressure, affects the band structure of the amorphous carbon nitride. This is due to the fact that the density affects the stress in the film, which also impacts the localized states in the band gap. These results are supported by density of states measurements using scanning tunneling spectroscopy.
State-specific studies of internal mixing in a prototypical flexible bichromophore: Diphenylmethane
Authors: Pillsbury Nathan R. , Stearns Jaime A. , Müller Christian W. , Plusquellic David F. , Zwier Timothy S.
Published: September 2008

Laser-induced fluorescence, resonant two-photon ionization, UV-UV hole burning, UV depletion, and single vibronic level fluorescence (SVLF) spectra of jet-cooled diphenylmethane (DPM) have been recorded over the 37 300–38 400 cm−1 region that encompasses the S1←S0 and S2←S0 transitions. All transitions in the laser-induced fluorescence excitation spectrum are due to a single conformational isomer of DPM with C2 symmetry. The S1←S0 origin transition occurs at 37 322 cm−1, supporting a short progression in the symmetric torsion T with spacing of 28 cm−1. The S2←S0 origin transition occurs 123 cm−1 above the S1 origin and possesses very weak torsional structure, observable only under saturating laser power conditions. A combination of SVLF spectroscopy and hot band studies is used to assign the frequencies of the symmetric torsion (T), antisymmetric torsion (T¯), and butterfly (β) vibrations in the S0, S1, and S2 states. The emission from the S2 origin is composed of two components, a set of sharp transitions ascribable to the S2 state and a dense “clump” of transitions ending in ground-state levels 81, 88, and 93 cm−1 above the S0 zero-point level ascribable to S1(v) emission. Assignment of the transitions in the clump leads to the conclusion that the single vibronic level responsible for the emission has mixed S2/S1 character. The mixing involves several torsional vibronic levels in the S1 manifold close in energy to the S2 origin, with the correct symmetry to couple the two states. These levels involve significant torsional excitation. The close energetic proximity of these levels leads to a breakdown of typical vibronic coupling selection rules.
Simulations of the protein folding process using topology-based models depend on the experimental structure
Authors: Prieto Lidia , Rey Antonio
Published: September 2008

Topology-based potentials (also known as Gō-type models) have been widely used in the study of the protein folding problem. When a topology-based potential is applied, the structure of the native state of the protein considered has to be known in advance. This fact gives to these models a semiempirical character, and therefore the quality of the simulation results obtained for the folding transition relies, among other factors, on the accuracy of the experimental structural data employed. In this work, we use a topology-based potential to carry out folding simulations of a protein whose structure has been determined both with NMR spectroscopy and x-ray crystallography. This way, we have been able to establish to which extent the differences in the topologies of the two experimental structures, easily ignored in a standard structural analysis for this protein, affect the thermodynamic characteristics of the folding transition defined in the simulations.
Electrical conduction and electroluminescence in nanocrystalline silicon-based light emitting devices
Authors: Prezioso S. , Anopchenko A. , Gaburro Z. , Pavesi L. , Pucker G. , Vanzetti L. , Bellutti P.
Published: September 2008

Electrical transport and light emission properties of plasma-enhanced chemical vapor deposition grown light emitting devices (LEDs) based on nanocrystalline silicon have been studied. Various active layer compositions have been used. Electroluminescence and current-voltage measurements have been performed on metal-oxide-semiconductor structures. We found that Poole–Frenkel emission and trap-assisted tunneling between traps located at the nanocrystalline silicon interfaces are consistent with the measurements. The interface trap density was estimated. Its dependence on the composition of the active layer is discussed. We propose an equivalent electrical circuit model for the LED based on complex impedance measurements. Nanocrystalline silicon electroluminescence in the near infrared region is explained by hot-electron injection and impact ionization mechanism. It is concluded that the trap-assisted tunneling and charge trapping limit the external power efficiency of this kind of devices.
Comparative x-ray reflectometry and atomic force microscopy of surfaces with non-Gaussian roughness
Authors: Mironov V. L. , Udalov O. G. , Gribkov B. A. , Fraerman A. A.
Published: September 2008

Theoretical and experimental investigations have been carried out with the aim of comparing atomic force microscopy (AFM) and x-ray reflectometry (XRR) as methods for characterizing surface roughness. It is shown that AFM gives more appropriate information about the surface roughness in comparison to XRR. The method for estimating the parameters that characterize x-ray scattering on the basis of AFM data is developed.
Investigation of plasma-dust structures in He-Ar gas mixture
Authors: Maiorov S. A. , Ramazanov T. S. , Dzhumagulova K. N. , Jumabekov A. N. , Dosbolayev M. K.
Published: September 2008

The paper reports on the first experiments with plasma-dust formations in dc gas discharge plasma for a He-Ar mixture. It is shown that the choice of light and heavy gases for the mixture suppresses ion heating in electric field under the conventional conditions of experiments and results in a supersonic jet with high Mach numbers. Distribution functions for drifting ions in the gas mixture are calculated for various mixture concentrations, electric field strengths, and gas pressures.
Coexistence of Eckhaus instability in forced zigzag Turing patterns
Authors: Berenstein Igal , Muñuzuri Alberto P.
Published: September 2008

Wavelength selection is an important feature in pattern forming systems. There are two distinct instabilities that arise when a mismatching wavelength is imposed on a pattern forming system, the Eckhaus instability (when the imposed wavelength is smaller than the preferred wavelength) and the zigzag instability (when the imposed wavelength is larger than the preferred wavelength). These two perhaps contradicting instabilities coexist in an experiment in which Turing patterns are forced with slowly moving stripes with a wavelength that is about 1.5 the wavelength of the Turing patterns. We also show that these two instabilities coupled together can lead to the reorientation of patterns under traveling stripe forcing.
Equilibrium calculation of the friction coefficient for a massive particle moving in finite liquid volume
Authors: Petravic Janka
Published: September 2008

It is well established that the Green–Kubo type of expression of the friction coefficient for a massive colloidal particle, i.e., the force autocorrelation integral, vanishes at long times if the liquid volume is finite. Here I show that the nonzero friction coefficient, defined as the ratio of force on the particle and the average liquid velocity, can be found in the framework of the linear response theory as the ratio of the force autocorrelation integral and the correlation integral of liquid velocity and force on the particle. The finite inverse friction coefficient can be alternatively expressed as the autocorrelation integral of the liquid velocity.
Semiclassical study of the one-dimensional hydrogen molecule
Authors: López-Castillo A.
Published: September 2008

The hydrogen molecule, as a restricted four-body problem, is a mixed chaotic system and is studied in this work as an extension of the helium atom. Several types of one-dimensional periodic orbits have been studied for this two-fixed-center system starting from some known orbits for the one-fixed-center system (helium atom). The hydrogen molecule has been studied by means of a semiclassical formalism. The single quantization of some periodic orbits are shown. These orbits are used to form a global quantization of the hydrogen molecule. Electronic energies of this nonintegrable molecular system are obtained with nonsingle semiclassical quantization.
Magnetic drift kinetic damping of the resistive wall mode in large aspect ratio tokamaks
Authors: Liu Yueqiang , Chu M. S. , Gimblett C. G. , Hastie R. J.
Published: September 2008

An analytical, large aspect ratio, calculation of the drift-kinetic energy perturbation is carried out for the resistive wall mode, due to the mode resonance with the magnetic precession drifts of trapped thermal ions and electrons. Four asymptotic cases are identified and analyzed in detail. Generally, a partial stabilization of the mode is possible thanks to the kinetic correction to the perturbed plasma energy. A complete stabilization can occur only in a narrow space of the plasma equilibrium parameters. Kinetic destabilization of the mode is also possible due to a finite pressure correction to the precession drift frequency.
Large amplitude internal solitary waves in a two-layer system of piecewise linear stratification
Authors: Goullet Arnaud , Choi Wooyoung
Published: September 2008

We study large amplitude internal solitary waves in a two-layer system where each layer has a constant buoyancy frequency (or Brunt–Väisälä frequency). The strongly nonlinear model originally derived by Voronovich [J. Fluid Mech. 474, 85 (2003)] under the long wave assumption for a density profile discontinuous across the interface is modified for continuous density stratification. For a wide range of depth and buoyancy frequency ratios, the solitary wave solutions of the first two modes are described in detail for both linear-constant and linear-linear density profiles using a dynamical system approach. It is found that both mode-1 and mode-2 solitary waves always point into the layer of smaller buoyancy frequency. The width of mode-1 solitary waves is found to increase with wave amplitude while that of mode-2 solitary waves could decrease. Mode-1 solitary wave of maximum amplitude reaches the upper or lower wall depending on its polarity. On the other hand, mode-2 solitary wave of maximum amplitude can reach the upper or lower wall only when the interface is displaced toward the shallower layer; otherwise, the maximum wave amplitude is smaller than the thickness of the deeper layer. Streamlines and various physical quantities including the horizontal velocity and the Richardson number are computed and discussed in comparison with the recent numerical solutions of the Euler equations by Grue et al. [J. Fluid Mech. 413, 181 (2000)].
A study of the phase transitions and structural chemistry of CsH3(SO4)2 and Cs3H(SO4)2 single crystals using H1 and C133s nuclear magnetic resonances
Authors: Lim Ae Ran , Chang Jin-Hae
Published: September 2008

The H1 and C133s spin-lattice and spin-spin relaxation times of CsH3(SO4)2 and Cs3H(SO4)2 single crystals were measured using nuclear magnetic resonance (NMR) near the phase transition temperatures of these crystals. CsH3(SO4)2 crystals undergo three phase transitions at high temperatures (TC1=320 K, TC2=420 K, and TC3=496 K), whereas Cs3H(SO4)2 undergoes four phase transitions (TC1=225 K, TC2=253 K, TC3=306 K, and TC4=419 K). The behavior of T1 for the H1 and C133s nuclei in the two crystals differs markedly. For CsH3(SO4)2, the H1 spin-lattice relaxation time increases with increasing temperature, whereas for Cs3H(SO4)2 this relaxation time decreases with increasing temperature. These results indicate that the molecular motion of H1 in the proton-rich CsH3(SO4)2 crystals differs from that of H1 in Cs3H(SO4)2 crystals. The changes in the H1 and C133s spin-lattice relaxation times at the phase transition temperatures result from changes in the environments of the H1 and C133s nuclei during the transitions. In addition, the spin-lattice relaxation times of the CsH3(SO4)2 and Cs3H(SO4)2 crystals indicate that they have superionic character above TC2 (=420 K) and TC1 (=225 K), respectively. Further, new hydrogen sulfates of alkaline metals are discussed in terms of their hydrogen-bonding systems. For compounds of formula CsXHNSO4 (where M is an alkali metal, X+N=2), the value of N gives the average number of hydrogen donor functions (OH groups) per SO4 tetrahedron. The N value defines the main features of the hydrogen-bonding systems.
On focusing of a ring ripple on a Gaussian electromagnetic beam in a plasma
Authors: Misra Shikha , Mishra S. K.
Published: September 2008

In this communication the authors have investigated the focusing of a ring ripple on a Gaussian electromagnetic beam propagating in a plasma, considering each of the three kinds of basic nonlinearities, namely, ponderomotive, collisional, and relativistic. In this analysis, the electric field profile of the propagating beam is assumed to be composed of the radial electric field distribution of the Gaussian beam as well as that of the ring ripple; a paraxial like approach has been adopted to analyze the characteristics of the propagation. Thus, one considers a unique dielectric function for the beam propagation and a radial field sensitive diffraction term, appropriate to the vicinity of the maximum of the irradiance distribution of the ring ripple. Further, the variation of the phase associated with the beam on account of the r independent terms in the eikonal has also been accounted for.
Linear stability analysis of inclined two-layer stratified flows
Authors: Negretti M. Eletta , Socolofsky Scott A. , Jirka Gerhard H.
Published: September 2008

Two-layer stratified flows are commonly observed in geophysical and environmental contexts. At the interface between the two layers, both velocity shear and buoyancy interplay, resulting in various modes of instability. Results from a temporal linear stability analysis of a two-layer stratified exchange flow under the action of a mean advection are presented, investigating the effect of a mild bottom slope on the stability of the interface. The spatial acceleration is directly included in the governing stability equations. The results demonstrate that increasing the bottom slope has a similar effect on the stability of the flow as does increasing the ratio R of the thickness of the velocity mixing layer δν to that of the density layer δρ as it causes the flow to be more unstable to the Kelvin–Helmholtz instabilities. The transition from Kelvin–Helmholtz modes to stable flow occurs at lower Richardson numbers and wavenumbers compared to the horizontal two-layer flow. Kelvin–Helmholtz modes are decreasingly amplified for 1<R<2. When 2<R<2, Kelvin–Helmholtz modes are first amplified and then damped as the Richardson number increases. This suggests that the behavior of the Richardson number alone is not sufficient to predict the stability tendency of the interface.
Rayleigh–Taylor instability growth on low-density foam targets
Authors: Watari T. , Nakai M. , Azechi H. , Sakaiya T. , Shiraga H. , Shigemori K. , Fujioka S. , Otani K. , Nagai K. , Sunahara A. , Nagatomo H. , Mima K.
Published: September 2008

In recent laser fusion programs, foam cryogenic targets have been developed as promising targets which have a great potential to realize efficient nuclear fusion. The foam is porous plastic material having a microstructure inside. We observed the growth of the Rayleigh–Taylor (RT) instability on the foam target with initial surface perturbation for the first time. The measured RT growth rate on the foam target was clearly suppressed in comparison to that of normal-density polystyrene (CH) targets. The values of the RT growth rate for the low-density foam target and the normal-density CH target were 0.84±0.15 (1∕ns) and 1.33±0.1 (1∕ns), respectively.
Simple equation of state for hard disks on the hyperbolic plane
Authors: López de Haro Mariano , Santos Andrés , Yuste Santos B.
Published: September 2008

A simple equation of state for hard disks on the hyperbolic plane is proposed. It yields the exact second virial coefficient and contains a pole at the highest possible packing. A comparison with another very recent theoretical proposal and simulation data is presented.
Continuous phase transition in the region of the vacuum arc cathode spot
Authors: Askari S. , Minoo H. , Moussakhani K.
Published: September 2008

A model for the near-cathode region of electric arcs is presented to investigate the liquid-plasma phase transition in the cathode spot region. Due to the high values of pressure and temperature after spot ignition, a “continuous phase transition” occurs in the liquid-vapor interface. A set of fluid equations with suitable boundary conditions have been solved to obtain diagrams of the spot plasma in the temperature-density plane during the spot evolution for a typical spot. To evaluate the model, the magnitude of some essential quantities such as the mean ion charge state of plasma and current density have been calculated, which are in accordance with experimental results.
Correlation between residual strain and electrically active grain boundaries in multicrystalline silicon
Authors: Chen Jun , Chen Bin , Sekiguchi Takashi , Fukuzawa Masayuki , Yamada Masayoki
Published: September 2008

We report the correlation between residual strain and electrically active grain boundaries (GBs) in multicrystalline silicon. The former concerns the process yield, and the latter affects the solar cell efficiency. The distribution of strain was imaged by scanning infrared polariscope, and the electrically active GBs were characterized by electron-beam-induced current. Large strain was detected near multitwin boundaries and small-angle GBs. The multitwin boundaries are electrically inactive, while small-angle GBs act as strong recombination centers. It indicates that the electrical activities of GBs are not directly related to the residual strain.
Zener tunneling in semiconducting nanotube and graphene nanoribbon p−n junctions
Authors: Jena Debdeep , Fang Tian , Zhang Qin , Xing Huili
Published: September 2008

A theory is developed for interband tunneling in semiconducting carbon nanotube and graphene nanoribbon p−n junction diodes. Characteristic length and energy scales that dictate the tunneling probabilities and currents are evaluated. By comparing the Zener tunneling processes in these structures to traditional Group IV and III–V semiconductors, it is proved that for identical bandgaps, carbon-based one-dimensional (1D) structures have higher tunneling currents. The high tunneling current magnitudes for 1D carbon structures suggest the distinct feasibility of high-performance tunneling-based field-effect transistors.
Tunable effective permittivity of carbon nanotube composites
Authors: Liu L. , Kong L. B. , Matitsine S.
Published: September 2008

Composites with carbon nanotubes (CNTs) as inclusions were prepared and the dielectric properties under bias voltages were studied. It was found that the composites with weight concentrations of CNTs above 6 wt % exhibited tunable dielectric characteristics under an external applied bias voltage with real part decreasing while the imaginary part increases with the increasing applied voltage. The tunable properties may be understood from the percolation threshold point of view. Potential applications of such tunable properties of the CNTs composites include smart materials and structures.
Enhancement of genetic diversity in canola-quality Brassica napus and B. juncea by interspecific hybridisation
Authors: Schelfhout C. J. , Wroth J. M. , Yan G. , Cowling W. A.
Published: September 2008

Reciprocal crosses were made between Brassica napus cv. Mystic (canola) and B. juncea JN29 (near canola quality). The F1 hybrids were selfed and backcrossed in all possible combinations to parent plants. The greatest number of selfed fertile progeny were obtained when Mystic was the maternal parent, and its F1 was most successful in backcrosses to Mystic or JN29 as maternal or paternal parent. The predominant morphological type of fertile progeny was B. napus, but several B. juncea morphological types occurred in F2 and BC1-derived lines. F2 : 3 and BC1S0 : 1 progeny showed transgressive segregation for agronomic and seed quality traits in two contrasting field environments. Several of the B. juncea-type progeny had improved seed quality (lower total seed glucosinolates and higher % oleic acid) over the B. juncea parent. Selfing of interspecific hybrids between canola-quality B. napus and B. juncea has the potential to greatly enhance genetic diversity in canola-quality progeny of both species, without the loss of donor alleles that normally occurs with repeated backcrossing.
Solvent retention capacities as indirect selection criteria for sugar snap cookie quality in Chinese soft wheats
Authors: Zhang Yong , Zhang Qijun , He Zhonghu , Zhang Yan , Ye Guoyou
Published: September 2008

Development of soft wheat cultivars with high sugar snap cookie quality is one of the most important breeding objectives in south China. Lack of an efficient criterion for selection for soft wheat quality is the main reason slowing genetic progress. Seventeen Chinese soft wheat genotypes grown at three locations in 2000–01 and 2001–02 wheat seasons in the Southern Winter Wheat Region, were used to investigate the potential of solvent retention capacity (SRC) parameters as indirect selection criteria for improving cookie diameter. All traits investigated displayed medium to high broad-sense heritability. Lactic acid SRC and sucrose SRC had the highest heritability, with the estimate being 0.92 and 0.86 on across-environment genotype mean value, while ranging from 0.93 to 0.99 and from 0.95 to 0.99, respectively, in the six individual environments. Sucrose SRC was highly significantly and negatively correlated with cookie diameter on both phenotypic and genotypic levels, with values of –0.86 (P < 0.001) and –0.91 (P < 0.001) on across-environment genotype performance, and ranging from –0.71 (P < 0.01) to –0.86 (P < 0.001) and from –0.79 (P < 0.001) to –0.93 (P < 0.001), respectively, in the six environments. Sucrose SRC was found to be a good selection criterion for improving cookie diameter. When applying the same intensity, genetic progress on cookie diameter achieved through sucrose SRC selection was as efficient as that for cookie diameter itself on across-environment genotype performance, while slightly less efficient on within-environment genotype performance, with the relative selection efficiency ranging from 0.81 to 0.90. Moreover, indirect selection through sucrose SRC was always more efficient than direct selection under the assumption of equivalent cost, with the relative efficiency of 1.52 based on across-environment selection, and ranged from 1.22 to 1.36 on within-environment selection.
Quantitative trait loci for water-soluble carbohydrates and associations with agronomic traits in wheat
Authors: Rebetzke G. J. , van Herwaarden A. F. , Jenkins C. , Weiss M. , Lewis D. , Ruuska S. , Tabe L. , Fettell N. A. , Richards R. A.
Published: September 2008

Several environmental factors including drought and disease can reduce leaf area and photosynthesis during grain-filling to decrease grain yield and kernel weight of cereal crops. Water-soluble carbohydrates (WSC) accumulated around anthesis can be mobilised to assist in filling of developing grains when post-anthesis assimilation is low. Cultivar differences support opportunities to select for high WSC but little is known of the extent or nature of genetic control for this trait in wheat. Three wheat mapping populations (Cranbrook/Halberd, Sunco/Tasman, and CD87/Katepwa) were phenotyped for WSC and other agronomic traits across multiple environments. The range for WSC concentration (WSC-C) was large among progeny contributing to moderate-to-high narrow-sense heritabilities within environments (h2 = 0.51–0.77). Modest genotype × environment interaction reduced the correlation of genotype means across environments (rp = 0.37–0.78, P < 0.01) to reduce heritability on a line-mean (h2 = 0.55–0.87) basis. Transgressive segregation was large and genetic control complex, with 7–16 QTLs being identified for WSC-C in each population. Heritability was smaller (h2 = 0.32–0.54) for WSC mass per unit area (WSC-A), reflecting large genotype × environment interaction and residual variance with estimating anthesis biomass. Fewer significant QTLs (4–8) were identified for this trait in each population, while sizes of individual genetic effects varied between populations but were repeatable across environments. Several genomic regions were common across populations including those associated with plant height (e.g. Rht-B1) and/or anthesis date (e.g. Ppd1). Genotypes with high WSC-C were commonly shorter, flowered earlier, and produced significantly (P < 0.01) fewer tillers than those of low WSC-C. This resulted in similar yields, lower final biomass, and fewer grains per m2, but greater dry weight partitioning to grain, kernel weight, and less grain screenings in high compared with low WSC-C genotypes. By contrast, lines high for WSC-A produced more fertile tillers associated with similar or greater anthesis and maturity biomass, grain number, and yield, yet similar kernel weight or size compared with genotypes with low WSC-A. The data support an important role for WSC-A in assuring stable yield and grain size. However, the small effects of many independent WSC QTLs may limit their direct use for marker-aided selection in breeding programs. We suggest using molecular markers to enrich populations for favourable height and anthesis date alleles before the more costly phenotypic selection among partially inbred families for greater WSC-A.
Field evaluation of phalaris, tall fescue and cocksfoot cultivars and accessions in western Victoria, Australia
Authors: Reed K. F. M. , Nie Z. N. , Clark B.
Published: September 2008

To assess their potential usefulness in the central and south-western Victorian environment, cultivars/experimental varieties and accessions of each of three perennial grasses, phalaris (Phalaris aquatica L.), tall fescue (Festuca arundinacea Schreb. = syn. Lolium arundinaceum. (Schreb.) Darbysh.), and cocksfoot (Dactylis glomerata L.), were established as swards by spring-sowing and then evaluated under rotational grazing by sheep. Pasture establishment, production, and survival following severe drought were measured at two locations. Persistent novel material of phalaris and tall fescue was identified that could increase the cool-season and year-round production relative to that obtained from current commercial cultivars.
Phalaris and tall fescue varieties were compared at Hamilton. Results indicated that, in contrast to tall fescue, the seedling vigour of winter-active phalaris types was similar in spring relative to that of summer-active types. Most phalaris cultivars were more productive than tall fescue in autumn and winter (P < 0.05). For the experimental phalaris variety Perla × Sirocco, dry matter (DM) production during these seasons was 19% greater than for the most productive tall fescue, cv. Fraydo (P < 0.05).
In a short growing season site at Warrak, winter-active cultivars of tall fescue produced up to 17% more DM in winter (P < 0.05) than the highest yielding, summer-active cv. Quantum MaxP, but for cumulative production over 3 years, Quantum MaxP was significantly more productive (P < 0.05) than 18 other entries. However, the persistence of Quantum and Quantum MaxP declined considerably post-drought; a more persistent accession from Sardinia, FA 005, was as productive as Quantum MaxP. Of the 13 cultivars compared in the longer growing season of Hamilton, Fraydo and Resolute MaxP were the most productive in winter (P < 0.05). For cumulative herbage yield over 4 years, Fraydo, Quantum MaxP, Quantum, Resolute MaxP, and Tanit were the most productive cultivars (P < 0.05). Infection with the MaxP endophyte did not affect persistence of Quantum at either site but improved the persistence of Resolute at Hamilton (P < 0.05). At Warrak, MaxP endophyte-infected Quantum was 35% more productive in summer–autumn than the endophyte-free cv. Quantum (P < 0.05).
Compared with the most productive commercial cv. Holdfast, experimental varieties from breeding populations of winter-active phalaris selected for grazing tolerance and which incorporated Perla, were superior for seedling vigour (rating 5 v. 3), winter growth (by ≥15%), and cumulative production over 4 years (≥12%) (P < 0.05).
Relating leaf photosynthetic rate to whole-plant growth: drought and shade effects on seedlings of four Quercus species
Authors: Quero José L. , Villar Rafael , Marañón Teodoro , Zamora Regino , Vega Dolores , Sack Lawren
Published: September 2008

Understanding the impacts of combined resource supplies on seedlings is critical to enable prediction of establishment growth, and forest dynamics. We investigated the effects of irradiance and water treatments on absolute growth, and relative growth rate (RGR) and its components, for seedlings of four Quercus species differing in leaf habit and with a wide variation in seed mass. Plants were grown for 6.5 months at three levels of irradiance (100, 27, and 3% daylight), and treated during the last 2.5 months with two watering treatments (frequent watering v. suspended watering). Both shade and drought reduced seedling growth rates, with a significant interaction: under full irradiance the drought treatment had a stronger impact on RGR and final biomass than under deep shade. For three species, seed mass was positively related to absolute growth, with stronger correlations at lower irradiance. The evergreen species grew faster than the deciduous species, though leaf habit accounted for a minor part of the interspecific variation in absolute growth. Seedling biomass was determined positively either by RGR or seed mass; RGR was positively linked with net assimilation rate (NAR) and leaf mass fraction (LMF), and seed mass was negatively linked with RGR and LMF, but positively linked with NAR. Seedling RGR was not correlated with light-saturated net photosynthetic rate, but was strongly correlated with the net carbon balance estimated, from photosynthetic light-response curves, considering daily variation in irradiance. These findings suggest an approach to applying short-term physiological measurements to predict the RGR and absolute growth rate of seedlings in a wide range of combinations of irradiance and water supplies.
Auxin: at the root of nodule development?
Authors: Mathesius Ulrike
Published: September 2008

Root nodules are formed as a result of an orchestrated exchange of chemical signals between symbiotic nitrogen fixing bacteria and certain plants. In plants that form nodules in symbiosis with actinorhizal bacteria, nodules are derived from lateral roots. In most legumes, nodules are formed de novo from pericycle and cortical cells that are re-stimulated for division and differentiation by rhizobia. The ability of plants to nodulate has only evolved recently and it has, therefore, been suggested that nodule development is likely to have co-opted existing mechanisms for development and differentiation from lateral root formation. Auxin is an important regulator of cell division and differentiation, and changes in auxin accumulation and transport are essential for lateral root development. There is growing evidence that rhizobia alter the root auxin balance as a prerequisite for nodule formation, and that nodule numbers are regulated by shoot-to-root auxin transport. Whereas auxin requirements appear to be similar for lateral root and nodule primordium activation and organ differentiation, the major difference between the two developmental programs lies in the specification of founder cells. It is suggested that differing ratios of auxin and cytokinin are likely to specify the precursors of the different root organs.
Magnetic-field effect on the photoactivation reaction of
Escherichia coli
DNA photolyase
Authors: Henbest Kevin B. , Maeda Kiminori , Hore P. J. , Joshi Monika , Bacher Adelbert , Bittl Robert , Weber Stefan , Timmel Christiane R. , Schleicher Erik
Published: September 2008

One of the two principal hypotheses put forward to explain the primary magnetoreception event underlying the magnetic compass sense of migratory birds is based on a magnetically sensitive chemical reaction. It has been proposed that a spin-correlated radical pair is produced photochemically in a cryptochrome and that the rates and yields of the subsequent chemical reactions depend on the orientation of the protein in the Earth's magnetic field. The suitability of cryptochrome for this purpose has been argued, in part, by analogy with DNA photolyase, although no effects of applied magnetic fields have yet been reported for any member of the cryptochrome/photolyase family. Here, we demonstrate a magnetic-field effect on the photochemical yield of a flavin–tryptophan radical pair in
Escherichia coli
photolyase. This result provides a proof of principle that photolyases, and most likely by extension also cryptochromes, have the fundamental properties needed to form the basis of a magnetic compass.
On avoiding dangerous anthropogenic interference with the climate system: Formidable challenges ahead
Authors: Ramanathan V. , Feng Y.
Published: September 2008

The observed increase in the concentration of greenhouse gases (GHGs) since the preindustrial era has most likely committed the world to a warming of 2.4°C (1.4°C to 4.3°C) above the preindustrial surface temperatures. The committed warming is inferred from the most recent Intergovernmental Panel on Climate Change (IPCC) estimates of the greenhouse forcing and climate sensitivity. The estimated warming of 2.4°C is the equilibrium warming above preindustrial temperatures that the world will observe even if GHG concentrations are held fixed at their 2005 concentration levels but without any other anthropogenic forcing such as the cooling effect of aerosols. The range of 1.4°C to 4.3°C in the committed warming overlaps and surpasses the currently perceived threshold range of 1°C to 3°C for dangerous anthropogenic interference with many of the climate-tipping elements such as the summer arctic sea ice, Himalayan–Tibetan glaciers, and the Greenland Ice Sheet. IPCC models suggest that ≈25% (0.6°C) of the committed warming has been realized as of now. About 90% or more of the rest of the committed warming of 1.6°C will unfold during the 21st century, determined by the rate of the unmasking of the aerosol cooling effect by air pollution abatement laws and by the rate of release of the GHGs-forcing stored in the oceans. The accompanying sea-level rise can continue for more than several centuries. Lastly, even the most aggressive CO
2
mitigation steps as envisioned now can only limit further additions to the committed warming, but not reduce the already committed GHGs warming of 2.4°C.
A collective mechanism for phase variation in biofilms
Authors: Chia Nicholas , Woese Carl R. , Goldenfeld Nigel
Published: September 2008

Understanding how microbes gather into biofilm communities and maintain diversity remains one of the central questions of microbiology, requiring an understanding of microbes as communal rather then individual organisms. Phase variation plays an integral role in the formation of diverse phenotypes within biofilms. We propose a collective mechanism for phase variation based on gene transfer agents, and apply the theory to predict the population structure and growth dynamics of a biofilm. Our results describe quantitatively recent experiments, with the only adjustable parameter being the rate of intercellular horizontal gene transfer. Our approach derives from a more general picture for the emergence of cooperation between microbes.
sparse inflorescence1
encodes a monocot-specific
YUCCA
-like gene required for vegetative and reproductive development in maize
Authors: Gallavotti Andrea , Barazesh Solmaz , Malcomber Simon , Hall Darren , Jackson David , Schmidt Robert J. , McSteen Paula
Published: September 2008

The plant growth hormone auxin plays a critical role in the initiation of lateral organs and meristems. Here, we identify and characterize a mutant,
sparse inflorescence1
(
spi1
), which has defects in the initiation of axillary meristems and lateral organs during vegetative and inflorescence development in maize. Positional cloning shows that
spi1
encodes a flavin monooxygenase similar to the
YUCCA
(
YUC
) genes of
Arabidopsis
, which are involved in local auxin biosynthesis in various plant tissues. In
Arabidopsis
, loss of function of single members of the
YUC
family has no obvious effect, but in maize the mutation of a single
yuc
locus causes severe developmental defects. Phylogenetic analysis of the different members of the
YUC
family in moss, monocot, and eudicot species shows that there have been independent expansions of the family in monocots and eudicots.
spi1
belongs to a monocot-specific clade, within which the role of individual
YUC
genes has diversified. These observations, together with expression and functional data, suggest that
spi1
has evolved a dominant role in auxin biosynthesis that is essential for normal maize inflorescence development. Analysis of the interaction between
spi1
and genes regulating auxin transport indicate that auxin transport and biosynthesis function synergistically to regulate the formation of axillary meristems and lateral organs in maize.
Arabidopsis
DRB4, AGO1, AGO7, and RDR6 participate in a DCL4-initiated antiviral RNA silencing pathway negatively regulated by DCL1
Authors: Qu Feng , Ye Xiaohong , Morris T. Jack
Published: September 2008

Plant RNA silencing machinery enlists four primary classes of proteins to achieve sequence-specific regulation of gene expression and mount an antiviral defense. These include Dicer-like ribonucleases (DCLs), Argonaute proteins (AGOs), dsRNA-binding proteins (DRBs), and RNA-dependent RNA polymerases (RDRs). Although at least four distinct endogenous RNA silencing pathways have been thoroughly characterized, a detailed understanding of the antiviral RNA silencing pathway is just emerging. In this report, we have examined the role of four DCLs, two AGOs, one DRB, and one RDR in controlling viral RNA accumulation in infected
Arabidopsis
plants by using a mutant virus lacking its silencing suppressor. Our results show that all four DCLs contribute to antiviral RNA silencing. We confirm previous reports implicating both DCL4 and DCL2 in this process and establish a minor role for DCL3. Surprisingly, we found that DCL1 represses antiviral RNA silencing through negatively regulating the expression of DCL4 and DCL3. We also implicate DRB4 in antiviral RNA silencing. Finally, we show that both AGO1 and AGO7 function to ensure efficient clearance of viral RNAs and establish that AGO1 is capable of targeting viral RNAs with more compact structures, whereas AGO7 and RDR6 favor less structured RNA targets. Our results resolve several key steps in the antiviral RNA silencing pathway and provide a basis for further in-depth analysis.
RIM1α phosphorylation at serine-413 by protein kinase A is not required for presynaptic long-term plasticity or learning
Authors: Kaeser Pascal S. , Kwon Hyung-Bae , Blundell Jacqueline , Chevaleyre Vivien , Morishita Wade , Malenka Robert C. , Powell Craig M. , Castillo Pablo E. , Südhof Thomas C.
Published: September 2008

Activation of presynaptic cAMP-dependent protein kinase A (PKA) triggers presynaptic long-term plasticity in synapses such as cerebellar parallel fiber and hippocampal mossy fiber synapses. RIM1α, a large multidomain protein that forms a scaffold at the presynaptic active zone, is essential for presynaptic long-term plasticity in these synapses and is phosphorylated by PKA at serine-413. Previous studies suggested that phosphorylation of RIM1α at serine-413 is required for presynaptic long-term potentiation in parallel fiber synapses formed
in vitro
by cultured cerebellar neurons and that this type of presynaptic long-term potentiation is mediated by binding of 14-3-3 proteins to phosphorylated serine-413. To test the role of serine-413 phosphorylation
in vivo
, we have now produced knockin mice in which serine-413 is mutated to alanine. Surprisingly, we find that in these mutant mice, three different forms of presynaptic PKA-dependent long-term plasticity are normal. Furthermore, we observed that in contrast to RIM1α KO mice, RIM1 knockin mice containing the serine-413 substitution exhibit normal learning capabilities. The lack of an effect of the serine-413 mutation of RIM1α is not due to compensation by RIM2α because mice carrying both the serine-413 substitution and a RIM2α deletion still exhibited normal long-term presynaptic plasticity. Thus, phosphorylation of serine-413 of RIM1α is not essential for PKA-dependent long-term presynaptic plasticity
in vivo
, suggesting that PKA operates by a different mechanism despite the dependence of long-term presynaptic plasticity on RIM1α.
Stra8
and its inducer, retinoic acid, regulate meiotic initiation in both spermatogenesis and oogenesis in mice
Authors: Anderson Ericka L. , Baltus Andrew E. , Roepers-Gajadien Hermien L. , Hassold Terry J. , de Rooij Dirk G. , van Pelt Ans M. M. , Page David C.
Published: September 2008

In eukaryotes, diploid cells give rise to haploid cells via meiosis, a program of two cell divisions preceded by one round of DNA replication. Although key molecular components of the meiotic apparatus are highly conserved among eukaryotes, the mechanisms responsible for initiating the meiotic program have diverged substantially among eukaryotes. This raises a related question in animals with two distinct sexes: Within a given species, are similar or different mechanisms of meiotic initiation used in the male and female germ lines? In mammals, this question is underscored by dramatic differences in the timing of meiotic initiation in males and females.
Stra8
is a vertebrate-specific, cytoplasmic factor expressed by germ cells in response to retinoic acid. We previously demonstrated that
Stra8
gene function is required for meiotic initiation in mouse embryonic ovaries. Here we report that, on an inbred C57BL/6 genetic background, the same factor is also required for meiotic initiation in germ cells of juvenile mouse testes. In juvenile C57BL/6 males lacking
Stra8
gene function, the early mitotic development of germ cells appears to be undisturbed. However, these cells then fail to undergo the morphological changes that define meiotic prophase, and they do not display the molecular hallmarks of meiotic chromosome cohesion, synapsis and recombination. We conclude that, in mice,
Stra8
regulates meiotic initiation in both spermatogenesis and oogenesis. Taken together with previous observations, our present findings indicate that, in both the male and female germ lines, meiosis is initiated through retinoic acid induction of
Stra8
.
Structural determinants for membrane association and dynamic organization of the hepatitis C virus NS3-4A complex
Authors: Brass Volker , Berke Jan Martin , Montserret Roland , Blum Hubert E. , Penin François , Moradpour Darius
Published: September 2008

Hepatitis C virus (HCV) NS3-4A is a membrane-associated multifunctional protein harboring serine protease and RNA helicase activities. It is an essential component of the HCV replication complex and a prime target for antiviral intervention. Here, we show that membrane association and structural organization of HCV NS3-4A are ensured in a cooperative manner by two membrane-binding determinants. We demonstrate that the N-terminal 21 amino acids of NS4A form a transmembrane α-helix that may be involved in intramembrane protein–protein interactions important for the assembly of a functional replication complex. In addition, we demonstrate that amphipathic helix α
0
, formed by NS3 residues 12–23, serves as a second essential determinant for membrane association of NS3-4A, allowing proper positioning of the serine protease active site on the membrane. These results allowed us to propose a dynamic model for the membrane association, processing, and structural organization of NS3-4A on the membrane. This model has implications for the functional architecture of the HCV replication complex, proteolytic targeting of host factors, and drug design.
Are there warlords in provincial Mozambique? Questions of the social base of MNR banditry
Authors: Darch Colin
Published: September 2008

Exploring the origins, nature and consequences of MNR violence and murder, this article argues that Renamo does not conform to the classical characteristics of warlordism. It does not represent a cession of central control to local interests; rather it is an attack on the national sovereignty of Mozambique created and perpetuated by external powers. Nevertheless, in some areas the externally imposed proxy war may have been able to achieve a certain local dynamic and so, to this extent, the warlord concept may have some limited usefulness. Darch also completely rejects the idea that the MNR can be considered to be a case of ‘social banditry’, even allowing for the weaknesses inherent in this concept.