bluuebunny/crossref_metadata_2025 huggingface dataset:
Scalar gradient and small-scale structure in turbulent premixed combustion
Authors: Kim Seung Hyun , Pitsch Heinz
Published: November 2007

Scalar gradient and small-scale structure in turbulent premixed combustion are investigated with emphasis on flame thickening. A Lagrangian-type equation for the evolution of the scalar gradient following an isoscalar surface is presented, which is useful in studying physical mechanisms for the scalar gradient evolution in premixed flames. The terms in the Lagrangian-type form of the scalar gradient equation are analyzed using direct numerical simulation data for statistically one-dimensional planar flames with high intensity turbulence. Two flames with Da<1 and Ka>1 are investigated. Results show that the curvature plays an important role in the evolution of the scalar gradient in turbulent premixed flames. The tangential strain rate, which is the major term to steepen the scalar gradient, is shown to be negatively correlated with the curvature due to the relation between the dilatation and the displacement speed of isoscalar surfaces. This represents the effects of heat release on the scalar gradient evolution. The relation between the dilatation and the displacement speed of isoscalar surfaces is also related to the presence of negative dilatation in premixed flames. The alignment characteristics of the flame normal with the principal axis of the strain are also investigated in relation to the characteristics of the tangential strain rate. Variations of the curvature, weighted by the density and the diffusivity, along the normal to the isosurfaces are found to be the major sink term in the scalar gradient equation and to have a negative correlation with the magnitude of the curvature. This provides evidence that smaller-scale wrinkling is more responsible for flame thickening. In the preheat zone, the tangential strain rate is balanced with the variation of the mass flux normal to the isosurface, and the strength of the thickening process is determined by the curvature variation term. In the reaction zone, the evolution of the scalar gradient is determined by the balance of the tangential strain rate and the curvature variation term. It is also shown that the thickening process in the reaction zone is much weaker than that in the preheat zone. In one of the simulated flames, a sudden drop of the strength of flame thickening in the reaction zone is observed.
Solvation potentials for flexible chain molecules in solution: On the validity of a pairwise decomposition
Authors: Taylor Mark P. , Petersen Gregory M.
Published: November 2007

The effects of a solvent on the conformation of a flexible n-site solute molecule can be described formally in terms of an n-body solvation potential. Given the practical difficulty in computing such multibody potentials, it is common to carry out a pairwise decomposition in which the n-body potential is approximated by a sum of two-body potentials. Here we investigate the validity of this two-site approximation for short interaction-site chain-in-solvent systems. Using exact expressions for the conformation of an isolated chain, we construct a mapping between the full chain-in-solvent system and its solvation potential representation. We present results for both hard-sphere and square-well systems with n=5 that show that the two-site approximation is sufficient to completely capture the effects of an explicit solvent on chain conformation for a wide range of conditions (which include varying the solvent diameter in the hard-sphere system and varying the chain-solvent coupling in the square-well system). In all cases, a set of two-site potentials (one for each distinct site-site pair) is required. We also show that these two-site solvation potentials can be used to accurately compute a multisite intramolecular correlation function.
High repetition rate laser produced soft x-ray source for ultrafast x-ray absorption near edge structure measurements
Authors: Fourmaux S. , Lecherbourg L. , Harmand M. , Servol M. , Kieffer J. C.
Published: November 2007

Recent progress in high intensity ultrafast laser systems provides the opportunity to produce laser plasma x-ray sources exhibiting broad spectrum and high average x-ray flux that are well adapted to x-ray absorption measurements. In this paper, the development of a laser based x-ray absorption near edge structure (XANES) beamline exhibiting high repetition rate by using the Advanced Laser Light Source (ALLS) facility 100Hz laser system (100mJ, 35fs at 800nm) is presented. This system is based on a broadband tantalum solid target soft x-ray source and a grazing incidence grating spectrometer in the 1–5nm wavelength range. To demonstrate the high potential of this laser based XANES technique in condensed matter physics, material science, or biology, measurements realized with several samples are presented: VO2 vanadium L edge, Si3N4 nitrogen K edge, and BPDA/PPD polyimide carbon K edge. The characteristics of this laser based beamline are discussed in terms of brightness, signal to noise ratio, and compared to conventional synchrotron broadband x-ray sources which allow achieving similar measurements. Apart from the very compact size and the relative low cost, the main advantages of such a laser based soft x-ray source are the picosecond pulse duration and the perfect synchronization between this x-ray probe and a laser pulse excitation which open the way to the realization of time resolved x-ray absorption measurements with picosecond range time resolution to study the dynamics of ultrafast processes and phase transition.
Phonon thermal conductivity in nanolaminated composite metals via molecular dynamics
Authors: Zhou Ya , Anglin Benjamin , Strachan Alejandro
Published: November 2007

We use nonequilibrium molecular dynamics to characterize the phonon contribution to thermal conduction of Al nanostructures and the role of interfaces in metallic nanocomposites. We characterize the lattice thermal conductivity of pure Al samples as a function of size and temperature from which we obtain, using kinetic theory, the temperature dependence of the phonon mean free path. We also calculated the thermal conductivity of Al∕Al* and Al∕Ni nanolaminate composites (where Al* differs from Al only in its mass) for various periodic sizes and compositions as well as the associated interfacial thermal resistivities (ITRs). We find that simple, additive models provide good estimates of the thermal conductivities of the nanocomposites in terms of those of the individual components and interfaces if size effects on the behavior of the individual components are considered. The additive models provide important insight to the decrease in thermal conductivity of the nanolaminates as their periodicity (thickness of a bilayer) is reduced to a size comparable with the phonon mean free path and break down when this characteristic size is reduced further. At this point the system can be regarded as homogeneous and the conductivity increases with decreasing periodicity of the laminates. We also observe that the ITR depends on the direction of the heat flux; this is the first molecular level characterization of such thermal diode behavior in a realistic three dimensional material.
Wang-Landau algorithm: A theoretical analysis of the saturation of the error
Authors: Belardinelli R. E. , Pereyra V. D.
Published: November 2007

In this work we present a theoretical analysis of the convergence of the Wang-Landau algorithm [Phys. Rev. Lett. 86, 2050 (2001)] which was introduced years ago to calculate the density of states in statistical models. We study the dynamical behavior of the error in the calculation of the density of states. We conclude that the source of the saturation of the error is due to the decreasing variations of the refinement parameter. To overcome this limitation, we present an analytical treatment in which the refinement parameter is scaled down as a power law instead of exponentially. An extension of the analysis to the N-fold way variation of the method is also discussed.
Similarity solution of mean streamwise flow along an external corner bisector
Authors: Moinuddin K. A. M. , Jones M. B. , Joubert P. N. , Chong M. S.
Published: November 2007

Turbulent boundary layer development, with zero pressure gradient, over an orthogonal external corner was investigated both experimentally and numerically. The results suggest that within the experimental and numerical limitations of the study that a similarity solution for the mean streamwise velocity profile exists along an external corner bisector. However, to confirm the self-similar solution, further independent measurement of the wall shear stress would be required. For the numerical simulation the Reynolds stress model was used. The experimental and numerical results were all consistent with a logarithmic self-similar solution. However the constants appearing in the self-similar solution were found to differ between the experimental and numerical results and reasons for these discrepancies are discussed. The results also provide scope for benchmarking of commercial software packages against a generic three-dimensional turbulent boundary layer that occurs in many engineering applications.
Modified configuration of relativistic magnetron with diffraction output for efficiency improvement
Authors: Daimon M. , Jiang W.
Published: November 2007

A modified configuration of relativistic magnetron with diffraction output has been proposed in order to improve microwave conversion efficiency. In this configuration, the microwave output coupling between the magnetron cavity and the cylindrical waveguide is significantly improved. Three-dimensional particle-in-cell simulations using simulation-code MAGIC were carried out to demonstrate the effectiveness of the modified configuration. In the simulation results, the maximum microwave efficiency of ∼37% has been obtained, compared with that of ∼3% obtained with conventional configuration.
Modeling the (HI)2 photodissociation dynamics through a nonadiabatic wave packet study of the I*–HI complex
Authors: López-López S. , Prosmiti R. , García-Vela A.
Published: November 2007

The nonadiabatic photodissociation dynamics of (HI)2 is simulated by applying a wave packet approach which starts from the I*–HI complex (where I* denotes the I(P1∕22) excited electronic state) produced after the photodissociation of the first HI moiety within (HI)2. In the model, two excited electronic potential surfaces corresponding to I*–HI(AΠ11) and I–HI(AΠ11), which interact through spin-rotation coupling, are considered. The simulations show that upon photodissociation of HI within I*–HI, the dissociating H fragment undergoes intracluster collisions with the I* atom. Some of these collisional events induce an electronically nonadiabatic transition which causes the deactivation of I* to the I ground electronic state. The probability of such nonadiabatic process is found to be 0.37%. Most of the photodissociation process takes place in the upper excited electronic surface [that of the I*–HI(AΠ11) complex], where H dissociation is found to be mainly direct or involving weak H∕I* intracluster collisions. These weak collisions with high collisional angular momentum, and therefore high collisional impact parameters associated, are responsible for most of the probability of nonadiabatic transitions found. The type of H∕I* collisions leading to nonadiabatic transitions appears to be closely related to the nature of the spin-rotation coupling between the two excited electronic states involved.
Phototriggering system for an ultrahigh-speed video microscopy
Authors: Karimov Pavel , Vo Le Cuong , Takehara Kohsei , Yokoi Sayoko , Etoh Takeharu Goji , Saitoh Yoshiharu
Published: November 2007

A phototrigger system is developed as a part of a video microscope mounting an ultrahigh-speed video camera capable of image capturing at frame rates as high as 1×106frames∕s. The extremely high frame rate is achieved by implementing in situ image storage. A distinguished feature of the camera is the on-chip overwriting mechanism that allows to keep in storage the latest image sequence of 103 frames; the old signals are continuously drained out of the storage. The trigger system is designed to synchronize recording operations with an occurrence of a target event within the limited image capturing duration. The target event is detected through a sudden change in the output of a sensor mounted to an optical port of the microscope. To reduce noise contribution, a two-sensor architecture is implemented. One sensor detects the target event while the one produces a reference signal used for noise reduction. Both sensors are connected to the same optical port by using a specially designed beam splitting unit. To provide high sensitivity, avalanche photodiodes are used as photoelements. System evaluation shows that its sensitivity is high and response time is less than 3μs. This is sufficiently fast for high-speed video-microscopy observations at 1×106frames∕s when using a video camera with a storage of 103 frames. As an example, the system was used in a microscopic observation of a soap film collapse.
Apparatus for real-time acoustic imaging of Rayleigh-Bénard convection
Authors: Kuehn Kerry , Polfer Jonathan , Furno Joanna , Finke Nathan
Published: November 2007

We have designed and built an apparatus for real-time acoustic imaging of convective flow patterns in optically opaque fluids. This apparatus takes advantage of recent advances in two-dimensional ultrasound transducer array technology; it employs a modified version of a commercially available ultrasound camera, similar to those employed in nondestructive testing of solids. Images of convection patterns are generated by observing the lateral variation of the temperature dependent speed of sound via refraction of acoustic plane waves passing vertically through the fluid layer. The apparatus has been validated by observing convection rolls in both silicone oil and ferrofluid.
Propagation of sinusoidal pulse laser beam in a plasma channel
Authors: Upadhyay Ajay K. , Raj Gaurav , Mishra Rohit K. , Jha Pallavi
Published: November 2007

The propagation of an intense sinusoidal pulse laser beam, in a preformed plasma channel having a parabolic density profile, is analyzed. Considering a nonparaxial, nonlinear wave equation and using a variational technique, simultaneous equations describing the evolution of laser spot and pulse length are obtained. Numerical methods are used to study the effect of pulse length variation on betatron oscillations of the laser spot size as it propagates in the plasma channel. Approximate conditions for propagation of the laser pulse with a constant spot size and pulse length (matched beam propagation) are obtained.
High-aspect ratio metal tips attached to atomic force microscopy cantilevers with controlled angle, length, and radius for electrostatic force microscopy
Authors: Cockins Lynda , Miyahara Yoichi , Stomp Romain , Grutter Peter
Published: November 2007

We demonstrate a method to fabricate a high-aspect ratio metal tip attached to microfabricated cantilevers with controlled angle, length, and radius, for use in electrostatic force microscopy. A metal wire, after gluing it into a guiding slot that is cut into the cantilever, is shaped into a long, thin tip using a focused ion beam. The high-aspect ratio results in considerable reduction of the capacitive force between tip body and sample when compared to a metal coated pyramidal tip.
Annealing of dilute-nitride GaAsSbN∕InP strained multiple quantum wells
Authors: Xu D. P. , Huang J. Y. T. , Park J. , Mawst L. J. , Kuech T. F. , Song X. , Babcock S. E.
Published: November 2007

The thermal annealing of GaAsSbN∕InP strained multiple quantum wells (MQWs) grown by metal organic chemical vapor deposition was investigated. Photoluminescence peak intensity and linewidth changes indicate a significant improvement in optical quality of the GaAsSbN∕InP MQWs upon annealing. We find no significant annealing-induced blueshift of the optical transitions, which confirms the theoretical expectation that a change in the nearest-neighbor configuration nitrogen atoms has negligible effect on the band gap of GaAsSbN. The evolution of (400) x-ray diffraction rocking curves with thermal treatment of the samples was consistent with the constituent redistribution in the GaAsSbN QW.
Quantum-confined and tunable optical emission from sub-10-nm silicon oxide nanowires in aqueous suspension
Authors: Zhang Z. Y. , Wu X. L. , Shen J. C. , Xu L. L. , Chu Paul K.
Published: November 2007

Silicon oxide nanowires (SiONWs) smaller than 10nm were synthesized by vaporization of SiO2 powders without catalytic assistance. The SiONWs resemble bamboos and the knots comprise Si nanocrystals of different orientations. A SiONW water suspension prepared ultrasonically was subjected to photoluminescence and photoluminescence excitation spectral examinations. Strong blue emission which arises from band-to-band recombination in the quantum confined Si nanocrystals in the knots is observed. Our results show that the emission characteristics can be tuned by adjusting the size of the knots.
An optically controlled phase shifter employing the organic semiconductor poly(3-hexylthiophene)
Authors: Tang Hongyan , Donnan R. S. , Kreouzis T.
Published: November 2007

The transmission characteristics of optically controlled phase shifters employing the organic semiconductor poly(3-hexylthiophene) (P3HT) are reported. Two microstrip structures were fabricated onto a P3HT coated indium tin oxide substrate supported by glass. Experimental results on these unoptimized prototype structures yield reversible differential phase shifts >10° at 2.0GHz under tens of milliwatt optical power illumination. These devices demonstrate great potential as linear analog phase shifters.
Hot electron relaxation and phonon dynamics in graphene
Authors: Butscher S. , Milde F. , Hirtschulz M. , Malić E. , Knorr A.
Published: November 2007

Using density-matrix theory, we microscopically calculate the relaxation dynamics of photoexcited electrons in graphene. Electron-phonon coupling leads to an initially ultrafast energy dissipation and to a nonthermal phonon occupation of the highest optical phonon modes. We also calculate the temporal evolution of the electronic temperature and find good agreement with recent experimental work.
Suppression of fatigue crack growth in carbon nanotube composites
Authors: Zhang W. , Picu R. C. , Koratkar N.
Published: November 2007

Fatigue is one of the primary causes for catastrophic failure in structural materials. Here, we report an order-of-magnitude reduction in the fatigue crack propagation rate for an epoxy system with the addition of ∼0.5wt.% of carbon nanotube additives. Using fractography analysis and fracture mechanics modeling, we show that the crack suppression is caused by crack bridging, which results in an effective crack-closing stress due to the pull out of nanotube fibers in the wake of the crack tip. Carbon nanotubes therefore show potential to significantly enhance the reliability and operating life of structural polymers that are susceptible to fatigue failure.
Direct ultraviolet excitation of an amorphous AlN:praseodymium phosphor by codoped Gd3+ cathodoluminescence
Authors: Maqbool Muhammad , Ahmad I. , Richardson H. H. , Kordesch M. E.
Published: November 2007

Sputter deposited thin film amorphous AlN:Pr (1at.%) emits in the blue-green (490–530nm) and red (∼650nm) regions of the visible spectrum under electron excitation. The addition of Gd 1at.% in the film enhances the blue emission by an order of magnitude. The enhancement in the blue region is a result of cathodoluminescence from Gd3+ at 313nm. The optical bandgap of amorphous AlN is about 210nm, so that the film is transparent in the ultraviolet, allowing the Gd emission to excite the Pr3+ ions. No significant quenching of the Gd emission is observed when the Gd and Pr ions are mixed. The blue enhancement is observed even with the two films containing each of the ions that are separated by a 500μm thick quartz spacer, showing that the enhancement is due entirely to UV radiation.
(
Na
0.5
Bi
0.5
)
0.87
Pb
0.13
Ti
O
3
thin films on different substrates for ferroelectric memory applications
Authors: Yang C. H. , Hu G. D. , Sun X. Q.
Published: November 2007

( Na 0.5 Bi 0.5 ) 0.87 Pb 0.13 Ti O 3 thin films have been prepared on Pt∕Ti∕SiO2∕Si and Bi2Ti2O7∕Si substrates using a metal organic decomposition method. The electrical measurements were conducted on metal-ferroelectric-metal or metal-ferroelectric-insulator-semiconductor capacitors. As Bi2Ti2O7 is an effective diffusion barrier, the leakage current and memory properties of (Na0.5Bi0.5)0.87Pb0.13TiO3∕Bi2Ti2O7∕Si are relatively improved. The polarization-electric field and capacitance-voltage measurements of (Na0.5Bi0.5)0.87Pb0.13TiO3 on Pt show good ferroelectric properties. The three phase transitions in (Na0.5Bi0.5)0.87Pb0.13TiO3 can be recognized by the change of capacitance with temperature.
Soldering to a single atomic layer
Authors: Girit Çağlar Ö. , Zettl A.
Published: November 2007

The standard technique to make electrical contact to nanostructures is electron beam lithography. This method has several drawbacks including complexity, cost, and sample contamination. We present a simple technique to cleanly solder submicron sized, Ohmic contacts to nanostructures. To demonstrate, we contact graphene, a single atomic layer of carbon, and investigate low- and high-bias electronic transport. We set lower bounds on the current carrying capacity of graphene. A simple model allows us to obtain device characteristics such as mobility, minimum conductance, and contact resistance.
Can soil amendments (zeolite or lime) shift the balance between nitrous oxide and dinitrogen emissions from pasture and wetland soils receiving urine or urea-N?
Authors: Zaman M. , Nguyen M. L. , Matheson F. , Blennerhassett J. D. , Quin B. F.
Published: November 2007

To determine the effects of soil amendments (lime or ammonium-sorbed zeolite) on emissions of nitrous oxide (N2O) and dinitrogen (N2) gases from pasture and wetland soils, a 90-day incubation experiment was conducted under controlled moisture and temperature conditions. Soil samples (0–0.10 m soil depth) collected from pasture and adjacent wetland sites were treated with 2 nitrogen (N) sources (cow urine or urea) at 200 kg N/ha with and without added soil amendments using 10-L plastic containers and then incubated at 25°C. Subsoil samples were taken out at different intervals to measure gaseous emissions of N2O and N2 using the acetylene (C2H2) inhibition method, ammonium (NH4+), nitrate (NO3–), soluble organic C, and pH. The anaerobic conditions (81% water-filled pore space) in wetland soils precluded nitrification, and therefore no increase in NO3–, N2O, or N2 was observed during the 90-day incubation period. In the pasture soil, the application of urine, urea, and soil amendments significantly affected daily and total N2O and N2 emissions and their ratios over a 90-day incubation period. Total N2O emission from urea-treated soil (48 kg N2O-N/ha) was significantly higher than from urine-treated soil (39 kg N2O-N/ha) and the control soil (4.5 kg N2O-N/ha). The application of zeolite significantly reduced N2O emissions from urea and urine-treated soils by 45% and 33%, respectively, due to the sorption of NH4+ by zeolite. Liming had minor effect on N2O emission. However, when lime was applied with zeolite, a significant reduction in N2O emission was observed. Lime application alone was found to increase N2 emissions in urine and urea treated soils by 46% and 35%, respectively, and thereby lower N2O : N2 ratios. The results indicate that zeolite reduced N2O emission while lime increased N2 emissions and lowered N2O : N2 ratios, and warranting further attention for mitigation of N2O.
The Brigalow Catchment Study: I. Overview of a 40-year study of the effects of land clearing in the brigalow bioregion of Australia
Authors: Cowie B. A. , Thornton C. M. , Radford B. J.
Published: November 2007

This paper describes a long-term, paired-catchment study, its broad findings, and considerations for future resource management of brigalow lands in north-eastern Australia. The Brigalow Catchment Study (BCS) commenced in 1965 with a pre-clearing calibration phase of 17 years to define the hydrology of 3 adjoining catchments (12–17 ha). After 2 catchments were cleared in 1982, 3 land uses (brigalow forest Acacia harpophylla, cropping, and grazed pasture) were monitored for water balance, resource condition and productivity, providing information for scientific understanding and resource management of the major land uses of the brigalow bioregion.
In addition, this paper draws upon several project reviews to highlight the value of the BCS as an ‘outdoor laboratory’, its data resource, and to reflect on the study’s scientific rigor to support present and future value. An assessment of the BCS against national and international attributes of best practice for long-term studies showed the study to rate highly in aspects of design, implementation, monitoring, and data management, and moderately in formal publication, strategic management, and networking. The literature shows that Brigalow Catchment Study is the longest paired-catchment study in Australia, and continues to sample the interactions between climate, soils, water, land use, and management.
Finally, this paper provides the context for component-specific papers on changes in hydrology, productivity, and salt balance. Results from the study to date include: a doubling of runoff after clearing, a reduction in wheat yield by more than 60% over 20 years, a halving of pasture availability 3 years after clearing, a decline in cattle liveweight gain of 4 kg/ha.year over an 8-year period with a constant stocking rate, and the leaching of 60% of the root-zone (0–1.5 m) chloride after clearing for cropping. Unanticipated applications of the data from the study include: (i) a crucial set of soil samples for calibration of the RothC soil carbon model used to estimate Australia’s soil carbon emissions; and (ii) estimates of deep drainage as a basis for salinity risk assessment in the region.
The Brigalow Catchment Study: II. Clearing brigalow (Acacia harpophylla) for cropping or pasture increases runoff
Authors: Thornton C. M. , Cowie B. A. , Freebairn D. M. , Playford C. L.
Published: November 2007

The Brigalow Catchment Study (BCS) was established to determine the impact on hydrology when brigalow land is cleared for cropping and grazing. The paired catchment study was commenced in 1965 using catchments of approximately 15 ha, with natural vegetation dominated by brigalow scrub (Acacia harpophylla). Three contiguous catchments were selected near Theodore in central Queensland to represent the extensive brigalow bioregion of central and southern Queensland and northern New South Wales (~40 Mha). The hydrology of the 3 catchments was characterised during a 17-year calibration period (1965–81). The catchments were considered hydrologically similar, with sufficient data available for an empirical comparison between catchments. In 1982, two of the catchments were cleared, with one developed for cropping and the other sown to improved pasture. The third catchment was used as an uncleared control. Hydrologic characteristics were then compared for the following 21 years. In their virgin state, the catchments behaved similarly, with average annual runoff being 5% of annual rainfall. Once cleared, total runoff from the cropping catchment increased to 11% of annual rainfall and total runoff from the pasture catchment increased to 9% of annual rainfall; however, timing of the individual runoff events varied between land uses. In order to confirm that changes in hydrology were a function of land use and not just seasonal variability or sampling error, several analytic techniques were used: a simple comparison of runoff totals, comparison of events, comparison of probability of exceedance for daily runoff, and comparison of predicted and observed runoff using a water balance modelling approach.
Powdery Mildew Induces Defense-Oriented Reprogramming of the Transcriptome in a Susceptible But Not in a Resistant Grapevine
Authors: Fung Raymond W.M. , Gonzalo Martin , Fekete Csaba , Kovacs Laszlo G. , He Yan , Marsh Ellen , McIntyre Lauren M. , Schachtman Daniel P. , Qiu Wenping
Published: November 2007

Grapevines exhibit a wide spectrum of resistance to the powdery mildew fungus (PM), Erysiphe necator (Schw.) Burr., but little is known about the transcriptional basis of the defense to PM. Our microscopic observations showed that PM produced less hyphal growth and induced more brown-colored epidermal cells on leaves of PM-resistant Vitis aestivalis ‘Norton’ than on leaves of PM-susceptible Vitis vinifera ‘Cabernet sauvignon’. We found that endogenous salicylic acid levels were higher in V. aestivalis than in V. vinifera in the absence of the fungus and that salicylic acid levels increased in V. vinifera at 120 h postinoculation with PM. To test the hypothesis that gene expression differences would be apparent when V. aestivalis and V. vinifera were mounting a response to PM, we conducted a comprehensive Vitis GeneChip analysis. We examined the transcriptome at 0, 4, 8, 12, 24, and 48 h postinoculation with PM. We found only three PM-responsive transcripts in V. aestivalis and 625 in V. vinifera. There was a significant increase in the abundance of transcripts encoding ENHANCED DISEASE SUSCEPTIBILITY1, mitogen-activated protein kinase kinase, WRKY, PATHOGENESIS-RELATED1, PATHOGENESIS-RELATED10, and stilbene synthase in PM-infected V. vinifera, suggesting an induction of the basal defense response. The overall changes in the PM-responsive V. vinifera transcriptome also indicated a possible reprogramming of metabolism toward the increased synthesis of the secondary metabolites. These results suggested that resistance to PM in V. aestivalis was not associated with overall reprogramming of the transcriptome. However, PM induced defense-oriented transcriptional changes in V. vinifera.
A Versatile Transposon-Based Activation Tag Vector System for Functional Genomics in Cereals and Other Monocot Plants
Authors: Qu Shaohong , Desai Aparna , Wing Rod , Sundaresan Venkatesan
Published: November 2007

Transposon insertional mutagenesis is an effective alternative to T-DNA mutagenesis when transformation through tissue culture is inefficient as is the case for many crop species. When used as activation tags, transposons can be exploited to generate novel gain-of-function phenotypes without transformation and are of particular value in the study of polyploid plants where gene knockouts will not have phenotypes. We have developed an in cis-activation-tagging Ac-Ds transposon system in which a T-DNA vector carries a Dissociation (Ds) element containing 4× cauliflower mosaic virus enhancers along with the Activator (Ac) transposase gene. Stable Ds insertions were selected using green fluorescent protein and red fluorescent protein genes driven by promoters that are functional in maize (Zea mays) and rice (Oryza sativa). The system has been tested in rice, where 638 stable Ds insertions were selected from an initial set of 26 primary transformants. By analysis of 311 flanking sequences mapped to the rice genome, we could demonstrate the wide distribution of the elements over the rice chromosomes. Enhanced expression of rice genes adjacent to Ds insertions was detected in the insertion lines using semiquantitative reverse transcription-PCR method. The in cis-two-element vector system requires minimal number of primary transformants and eliminates the need for crossing, while the use of fluorescent markers instead of antibiotic or herbicide resistance increases the applicability to other plants and eliminates problems with escapes. Because Ac-Ds has been shown to transpose widely in the plant kingdom, the activation vector system developed in this study should be of utility more generally to other monocots.
Nitrate Efflux at the Root Plasma Membrane: Identification of anArabidopsisExcretion Transporter
Authors: Segonzac Cécile , Boyer Jean-Christophe , Ipotesi Emilie , Szponarski Wojciech , Tillard Pascal , Touraine Brigitte , Sommerer Nicolas , Rossignol Michel , Gibrat Rémy
Published: November 2007

Root NO3  − efflux to the outer medium is a component of NO3  − net uptake and can even overcome influx upon various stresses. Its role and molecular basis are unknown. Following a functional biochemical approach, NAXT1 (for NITRATE EXCRETION TRANSPORTER1) was identified by mass spectrometry in the plasma membrane (PM) of Arabidopsis thaliana suspension cells, a localization confirmed using a NAXT1–Green Fluorescent Protein fusion protein. NAXT1 belongs to a subclass of seven NAXT members from the large NITRATE TRANSPORTER1/PEPTIDE TRANSPORTER family and is mainly expressed in the cortex of mature roots. The passive NO3  − transport activity (K  m = 5 mM) in isolated root PM, electrically coupled to the ATP-dependant H+-pumping activity, is inhibited by anti-NAXT antibodies. In standard culture conditions, NO3  − contents were altered in plants expressing NAXT-interfering RNAs but not in naxt1 mutant plants. Upon acid load, unidirectional root NO3  − efflux markedly increased in wild-type plants, leading to a prolonged NO3  − excretion regime concomitant with a decrease in root NO3  − content. In vivo and in vitro mutant phenotypes revealed that this response is mediated by NAXT1, whose expression is upregulated at the posttranscriptional level. Strong medium acidification generated a similar response. In vitro, the passive efflux of NO3  − (but not of Cl−) was strongly impaired in naxt1 mutant PM. This identification of NO3  − efflux transporters at the PM of plant cells opens the way to molecular studies of the physiological role of NO3  − efflux in stressed or unstressed plants.
SAD2, an Importin β-Like Protein, Is Required for UV-B Response in Arabidopsis by Mediating MYB4 Nuclear Trafficking
Authors: Zhao Jinfeng , Zhang Wenhui , Zhao Yang , Gong Ximing , Guo Lei , Zhu Guoli , Wang Xuechen , Gong Zhizhong , Schumaker Karen S. , Guo Yan
Published: November 2007

We report that the Arabidopsis thaliana mutant sensitive to ABA and drought2 (sad2), which harbors a T-DNA insertion in an importin β-like gene, is more tolerant to UV-B radiation than the wild type. Analysis of cyclobutane pyrimidine dimer accumulation revealed that less DNA damage occurred in sad2 than in the wild type during UV-B treatment. No significant growth difference was observed between sad2 and the wild type when treated with the genotoxic drug methyl methanesulfonate, suggesting that SAD2 functions in UV-B protection rather than in DNA damage repair. Whereas the R2R3-type transcription repressor MYB4 has previously been shown to negatively regulate the transcription of cinnamate 4-hydroxylase (C4H) and thus to regulate the synthesis of sinapate esters, expression of both MYB4 and C4H and accumulation of UV-absorbing compounds were significantly higher in sad2 than in the wild type. MYB4 did not localize to the nucleus in the sad2 mutant, suggesting that SAD2 is required for MYB4 nuclear trafficking. SAD2 and MYB4 coimmunoprecipitated, indicating that these proteins localize in the same complex in vivo. MYB4 protein specifically bound to its own promoter in gel shift assays and repressed its own expression, demonstrating that MYB4 protein and mRNA are part of a negative autoregulatory loop. This feedback loop is altered in the sad2 mutant due to the absence of MYB4 protein in the nucleus, leading to the constitutive expression of MYB4 and C4H and resulting in accumulation of UV-absorbing pigments that shield the plant from UV-B radiation.
Evolution and Function of acis-Regulatory Module for Mesophyll-Specific Gene Expression in the C4 DicotFlaveria trinervia
Authors: Akyildiz Meryem , Gowik Udo , Engelmann Sascha , Koczor Maria , Streubel Monika , Westhoff Peter
Published: November 2007

C4 photosynthesis presents a sophisticated integration of two complementary cell types, mesophyll and bundle sheath cells. It relies on the differential expression of the genes encoding the component enzymes and transporters of this pathway. The entry enzyme of C4 photosynthesis, phosphoenolpyruvate carboxylase (PEPC), is found exclusively in mesophyll cells, and the expression of the corresponding gene is regulated at the transcriptional level. In the C4 dicot Flaveria trinervia, the mesophyll-specific expression of the C4 PEPC gene (ppcA) depends on a 41-bp segment in the distal promoter region referred to as MEM1 (for mesophyll expression module1). Here, we show that a MEM1 sequence found in the orthologous ppcA gene from the C3 species Flaveria pringlei is not able to direct mesophyll-specific gene expression. The two orthologous MEM1 sequences of F. pringlei and F. trinervia differ at two positions, a G-to-A exchange and the insertion of the tetranucleotide CACT. Changes at these two positions in the C3 MEM1 sequence were necessary and sufficient to create a mesophyll-specificity element during C4 evolution. The MEM1 of F. trinervia enhances mesophyll expression and concomitantly represses expression in bundle sheath cells and vascular bundles.
In situsynchrotron powder diffraction study of active belite clinkers
Authors: De la Torre Ángeles G. , Morsli Khadija , Zahir Mohammed , Aranda Miguel A.G.
Published: November 2007

The clinkerization processes to form belite clinkers, with theoretical compositions close to 60 wt% of Ca2SiO4, have been studiedin situby high-resolution high-energy (λ = 0.30 Å) synchrotron X-ray powder diffraction. In order to obtain active belite cements, different amounts of K2O, Na2O and SO3have been added. The existence range of the high-temperature phases has been established and, furthermore, Rietveld quantitative phase analyses at high temperature have been performed for all patterns. The following high-temperature reactions have been investigated: (i) polymorphic transformations of dicalcium silicate, \alpha_{\rm L}'-Ca2SiO4↔ \alpha_{\rm H}'-Ca2SiO4from 1170 to 1230 K, and \alpha_{\rm H}'-Ca2SiO4↔ α-Ca2SiO4from 1500 to 1600 K; (ii) melting of the aluminates phases, Ca3Al2O6and Ca4(Al2Fe2)O10, above ∼1570 K; and (iii) reaction of Ca2SiO4with CaO to yield Ca3SiO5above ∼1550 K. Moreover, in all the studied compositions the temperature of the polymorphic transformation \alpha_{\rm H}'-Ca2SiO4↔ α-Ca2SiO4has decreased with the addition of activators. Finally, active belite clinkers were produced as the final samples contained α-belite phases.
Illustrated Fourier transforms for crystallography
Authors: Aubert Emmanuel , Lecomte Claude
Published: November 2007

Concepts such as Fourier transformation, convolution and resolution that are required to understand crystallography are illustrated through visual examples. These concepts can be explained pedagogically in a very direct way using theDigitalMicrographsoftware from Gatan Inc. (http://www.gatan.com/imaging/downloads.php), originally intended for electron microscopy data collection and analysis, and practical exercises developed around this tool can be used in teaching crystallography.
Advances in spectroscopic methods for biological crystals. 1. Fluorescence lifetime measurements
Authors: Royant Antoine , Carpentier Philippe , Ohana Jérémy , McGeehan John , Paetzold Bernhard , Noirclerc-Savoye Marjolaine , Vernède Xavier , Adam Virgile , Bourgeois Dominique
Published: November 2007

Synchrotrons are now producing thousands of macromolecular structures each year. The need for complementary techniques available on site has progressively emerged, either to assess the relevance of the structure of a protein or to monitor changes that may occur during X-ray diffraction data collection. Microspectrophotometers in the UV–visible absorbance or fluorescence mode have evolved over the past few decades to become the instruments of choice to perform such tests. Described here are recent improvements to the microspectrophotometer of the so-called Cryobench laboratory located at the European Synchrotron Radiation Facility, Grenoble, France. Optical and mechanical properties have been enhanced so as to record better spectra on smaller samples. A device has been implemented to measure the signal decay of fluorescent samples, either in the crystalline or in the solution state. Recording of the fluorescence lifetime in addition to the steady-state fluorescence emission spectrum allows precise monitoring of the fluorescent sample under study. The device consists of an adaptation of a commercially available time-correlated single-photon-counting (TCSPC) system. A method to record and analyze series of TCSPC histograms,e.g.collected as a function of temperature, is described. To validate the instruments, fluorescence lifetimes of fluorescent small molecules or proteins in the crystalline or solution state, at room and cryo temperatures, have been measured. Lifetimes of a number of fluorescent proteins of the GFP family were generally found to be shorter in crystals than in solution, and slightly longer at cryo temperatures than at ambient temperature. The possibility of performing fluorescence lifetime measurements on crystals at synchrotron facilities widens the variety of spectroscopic techniques complementing X-ray diffraction on macromolecular crystallography beamlines.
Variable-temperature X-ray crystal structure determinations of {Fe[tren(6-Mepy)3]}(ClO4)2and {Zn[tren(6-Mepy)3]}(ClO4)2compounds: correlation of the structural data with magnetic and Mössbauer spectroscopy data
Authors: Seredyuk Maksym , Gaspar Ana B. , Kusz Joachim , Bednarek Gabriela , Gütlich Philipp
Published: November 2007

Variable-temperature X-ray crystal structure determinations (80–330 K) on compounds {Fe[tren(6-Mepy)3]}(ClO4)2(1-Fe) {tren(6-Mepy)3is tris[3-aza-4-(6-methyl-2-pyridyl)but-3-enyl]amine} and {Zn[tren(6-Mepy)3]}(ClO4)2(1-Zn) {tren(6-Mepy)3is tris[3-aza-4-(6-methyl-2-pyridyl)but-3-enyl]amine} were carried out together with a detailed analysis of the unit-cell volume and parameters in the spin transition region for (1-Fe). Both compounds crystallize in the monoclinic system and retained the space groupP21/cat all measured temperatures. The Fe and Zn atoms are surrounded by six N atoms belonging to imine groups and pyridine groups of the trifurcated ligand, adopting a pseudo-octahedral symmetry. The average Fe—N bond lengths of 2.013 (1) Å (80 K) and 2.216 (2) Å (330 K) are consistent with a low-spin (LS) and a high-spin (HS) state for the iron(II) ions. In contrast to (1-Fe), the structures of (1-Zn) at low and high temperatures are similar and repeat the structural features of the high-spin structure of (1-Fe). The volume of the unit cell increases on heating from 80 to 330 K for (1-Fe) and (1-Zn). On the other hand, while thea,bandccell parameters increase for (1-Fe), they show less variation for (1-Zn). For (1-Fe), variation of the unit-cell volume with temperature recalculated per Fe atom shows a change ΔV= 27.16 Å3during the spin crossover process. Magnetic susceptibility and Mössbauer spectroscopy studies performed on (1-Fe) reveal an inversion temperature,T1/2of 233 K, where the molar fractions of LS and HS sites are both equal to 0.5. The variation in metal–ligand bond lengths, the distortion parameters and the cell parameters are very close to the character of the magnetic curve and the curve of γHS(the molar fraction of HS molecules) derived from the Mössbauer data; this result shows the correlation between structure and physical properties in (1-Fe).
Money demand function for Southeast Asian countries
Authors: Cheong Tang Tuck
Published: November 2007

Purpose

The purpose of this paper is to empirically investigate the money demand function for five Southeast Asian countries, viz. Malaysia, Thailand, Singapore, the Philippines, and Indonesia.

Design/methodology/approach

The ARDL modeling approach is employed because of its ability to incorporate both I(0) and I(1) regressors.

Findings

The results reveal that real M2 aggregate, real expenditure components, exchange rate, and inflation rate are cointegrated for Malaysia, the Philippines, and Singapore. The statistical significance of real income components suggests the bias of using single real income variable in money demand (M2 aggregate) specification of both short‐ and long‐run. The CUSUM and CUSUMSQ tests show that the estimated parameters are stable for the five Southeast Asian economies, except for Indonesia which is based on short‐run specification.

Practical implications

These findings are important for policy makers in formulating monetary policy.

Originality/value

Besides conventional determinants of money demand such as exchange rate and interest rate variables, this study considers the major components of final expenditure (GDP) – final consumption expenditures (private and government sectors), expenditures on investment goods, and exports as scale variables.
Export performance of developing countries under the Africa Growth and Opportunity Act
Authors: Seyoum Belay
Published: November 2007

Purpose

The purpose of this study is to assess the implications of US trade preferences under the African Growth and Opportunity Act (AGOA) and its impact on beneficiary country exports.

Design/methodology/approach

The approach is to use Wilcoxon signed rank test and time series regression analysis using ARIMA.

Findings

The results largely indicate that AGOA has a positive but not significant effect on beneficiary exports to the USA for all country groups. Its effect is also quite marginal on sectoral exports except for textiles and apparel. Similarly, AGOA's effect is positive but not significant for all major exporters except Lesotho.

Originality/value

A proper understanding of this relationship will help donors and recipients devise appropriate policies to help encourage the growth and diversification of exports that is so vital for developing countries.
Career success
Authors: Ballout Hassan I.
Published: November 2007

Purpose

The purpose of this paper is to review relevant literatures on career success and develop a theoretical framework and testable propositions concerning how human capital, person‐environment fit and organizational support relate to career success. Whilst acknowledging the substantial literature that has accumulated regarding the various antecedents and operationalizations involved in employees' career success, there is little research as how person‐environment fit and career success are related.

Design/methodology/approach

Literature outlining approaches to career success is summarized and research at the intersection of person‐environment fit and organizational support/career success are reviewed. This is followed by a set of propositions based upon the antecedents of career success.

Findings

It is suggested that person‐environment fit and organizational support are important antecedents of career success. Knowledge of career changes and these antecedents help individuals and organizations manage career success.

Research limitations/implications

Future research should examine empirically the linkages suggested by the paper along with other relationships asserted or implied by person‐environment fit and career success literature as mentioned in the paper.

Practical implications

Both employers and employees may benefit from integrating different types of fit into the psychological contract because each fit will impact aspects of career success. Therefore, organizations need to select and develop employees that can easily adjust and fit into careers that are compatible with their work environments.

Originality/value

This paper contributes to the literature by being one of the first to examine the effects of different types of person‐environment fit on career success.