bluuebunny/crossref_metadata_2025 huggingface dataset:
Ghost effect and bifurcation in a gas between coaxial circular cylinders with different temperatures
Authors: Sone Yoshio , Handa Masato , Doi Toshiyuki
Published: September 2003

A gas in a time-independent state between rotating coaxial circular cylinders with different temperatures is considered. The bifurcation of the field in the continuum limit is studied on the basis of the system of fluid-dynamic-type equations and their boundary conditions derived from the Boltzmann system [Phys. Fluids 8, 628 (1996)]. When the ratio of the temperatures of the two cylinders is not close to unity, the bifurcation occurs at infinitesimal speeds of rotation of the cylinders of the first order of the Knudsen number. The temperature field in the continuum limit is determined together with the infinitesimal velocity field, and a bifurcated temperature field, as well as an axially uniform and symmetric field, exists in the absence of the flow velocity (ghost effect). Further, thermal stress, as well as viscous stress, produces a finite effect on the bifurcated temperature field (a non-Navier–Stokes effect). For example, when the ratio of the temperatures of the two cylinders is ten or one tenth, the non-Navier–Stokes effect on the bifurcated temperature field amounts to 10%.
The effect of the Earth’s rotation on the transient amplification of disturbances in pipe flow
Authors: Bergström Lars B.
Published: September 2003

In pipe flow, for large Reynolds numbers, Draad and Nieuwstadt [J. Fluid Mech. 361, 297 (1998)] showed that the small Coriolis force due to the Earth’s rotation may affect the mean flow profile of liquids substantially. In this paper, the development of small disturbances superimposed on a laminar mean flow affected by the Coriolis force is investigated analytically. The investigation is focused on the time development and the transient growth of streamwise-independent disturbances since they are the most amplified disturbances without the Coriolis effect included. The results show that the modification of the parabolic mean flow caused by the Coriolis force significantly affects the transient disturbance amplification when the Reynolds number (R) is high. For example, with R=9000 and the Ekman number Ek=5.23, due to the Coriolis effect, the peak value of the transient disturbance amplification becomes about two-thirds of the peak value obtained in the case where the mean flow is unaffected by the Coriolis force. When the Reynolds number is decreased, the reduction of the transient growth becomes smaller.
Influence of wall shape on vortex formation in modulated channel flow
Authors: Zhou H. , Martinuzzi R. J. , Khayat R. E. , Straatman A. G. , Abu-Ramadan E.
Published: September 2003

The flow inside channels with periodic, wavy walls of arbitrary shape is considered numerically. Solutions are obtained using either a perturbation approach, for weak modulation amplitude, or a finite volume technique, for strong amplitude. The flow is examined for sinusoidal, arched and triangular modulation over a wide range of amplitude, wavelength and Reynolds number in the steady laminar regime. For weak wall modulation (ε<0.3, α<2, where ε and α are the dimensionless half-wave height and wavelength, respectively), it is found that the flow behavior along the modulated wall is of the boundary-layer type. As such, the critical Reynolds number, Rec, for separation for each modulation shape can be expressed as an explicit function of ε and α, while the location of separation and pressure distribution along the modulated wall scale with ε, α, and Rec. For strong modulations, the boundary layer model is no longer satisfactory to predict the flow behavior and deviations from the trends found for weaker modulations are observed. It is also shown that the driving force required to sustain a given flow rate increases as ε increases. For all modulation amplitudes, the sinusoidal wave shape is found to require the largest pressure gradient to maintain a given flow rate through the channel and, consequently, yields the highest friction factor. Finally, the existence of a stable recirculating flow regime is discussed in the light of earlier stability analyses.
Transition of a moving contact line from smooth to angular
Authors: Ben Amar M. , Cummings L. J. , Pomeau Yves
Published: September 2003

We consider the motion of a small droplet sliding under gravity down an inclined plane. Experimentally [see T. Podgorski, Thèse, Université Paris 6 (October 2000); T. Podgorski et al., Phys. Rev. Lett. 87, 036102 (2001)] it has been observed that such a droplet will develop an angular point in the contact line at its rear if its velocity is sufficiently high (i.e., if the plane is inclined sufficiently steeply to the horizontal). The angular point first appears at some critical, or threshold speed, Uc, and the angular discontinuity observed increases monotonically from zero at U=Uc. We seek to describe this phenomenon using a simple mathematical model based on lubrication theory. In the subcritical regime we find an exact solution to our model: a drop of circular perimeter sliding steadily down the inclined plane. This allows us to predict the formation of a nonanalyticity in the contact line at a well-defined critical droplet speed. For speeds just beyond this, we construct a local solution valid near the singular point, for which the angle in the contact line predicted by our theory agrees with the experimental results. We also construct a local solution in the fully developed critical regime, for sliding speeds well above critical, which is suggestive of a further bifurcation, also observed in the experiments [T. Podgorski, Thèse, Université Paris 6 (October 2000)].
A numerical study of open atmospheric balloon dynamics
Authors: Alexander Peter
Published: September 2003

The dynamics of open balloons in an atmosphere may be studied with a body-fluid coupled model. A numerical approach is required to solve the corresponding equation set. Solutions under different conditions are obtained here for the vertical and one horizontal direction. Relevant dynamical features during ascent, flotation, and descent depend on balloon thermodynamics, wind, air small-scale turbulence, and perturbations to the background atmosphere. After analysis of the results it is found that approximate analytical solutions may be found in certain cases. The effect of nonlinear drag on balloon oscillation period and damping near flotation is evaluated.
Electrohydrodynamically driven chaotic mixing in a translating drop. II. Experiments
Authors: Ward T. , Homsy G. M.
Published: September 2003

We investigate experimentally the mixing inside of settling drops in spatially uniform time-dependent electric fields. Though the Reynolds and Stokes numbers are small, the combined flow field can produce complex patterns via chaotic advection. These complex structures are visualized and examined by illuminating passive particles injected in translating drops, and the results are compared with numerical particle simulations. A silicone oil/castor oil system is used for the dispersed and continuous phases, respectively. Drop sizes are typically on the order of 5–6 mm in diameter under nearly isopycnic conditions, the small difference yielding a finite settling velocity. The electric field values are typically modulated between 3–10 kV at frequencies ranging from 0.01–0.05 Hz. The results presented show excellent agreement with the numerical results despite several conditions that need to be satisfied for the quasistatic approximation used in the analysis.
Pressure-strain correlation in homogeneous anisotropic turbulence subject to rapid strain-dominated distortion
Authors: Girimaji S. S. , Jeong E. , Poroseva S. V.
Published: September 2003

Rapid distortion calculations of initially anisotropic turbulence are performed to better understand the physics of the pressure-strain correlation in strain-dominated mean flows. Based on the results of simulations we infer important physical characteristics of the “rapid” pressure-strain correlation Φij(r) in such flows: (i) it vanishes when there is no production of anisotropy, (ii) in the proximity of two-componential state it tends to decrease Reynolds stress anisotropy, and (iii) its magnitude is generally smaller than that of production. The observed characteristics are proposed as criteria that pressure-strain correlation models may be required to satisfy. All of the current popular models violate the above criteria for a sizeable subset of anisotropic initial conditions. Reynolds stress transport model calculations show that unphysical and unrealizable model behavior can be directly attributed to these violations.
Distribution of density of photonic states in amorphous photonic materials
Authors: Wang Yiquan , Cheng Bingying , Zhang Daozhong
Published: September 2003

The density of states (DOS) and local density of states (LDOS) for an amorphous photonic material (APM) with a finite size and constructed by hexagonal basic cells are simulated. It is found that there is a frequency interval in which the total DOS is very small, i.e., a photonic gap exists. Near the gap-center frequency, the LDOS drops rapidly from the edge to the center area of the sample. However, at the gap-edge frequency, some discrete spots with high LDOS spread in the sample and corresponding electric field distributions show the occurrence of localized modes. This phenomenon can be attributed to the disordered distribution of the scatterers.
Spin splitting in narrow InAs quantum wells with In0.75Ga0.25As barrier layers
Authors: Möller C. H. , Heyn Ch. , Grundler D.
Published: September 2003

Using two independent magnetotransport experiments, i.e., thermal activation and the coincidence method in tilted fields, we determine the g factor in a two-dimensional electron system in a 4-nm-wide InAs quantum well. From these independent techniques we deduce consistently an absolute value |gexp|≅6. This is considerably smaller if compared to |g|=14.8 for bulk InAs. Nonparabolicity in InAs cannot fully explain the reduced g factor. We argue that the penetration of the wave function into the In0.75Ga0.25As barriers and into the In0.75Al0.25As spacer layer plays an additional role.
Cohesion in ball lightning
Authors: Gilman J. J.
Published: September 2003

The phenomenon of ball lightning has been observed for a long time, but the nature of these luminous balls has been unknown. It is proposed here that they consist of highly excited Rydberg atoms with large polarizabilities. Thus, the cohesion of the balls comes from photon exchange forces (London dispersion forces) rather than the more usual electron exchange (chemical) forces. The cohesion in plasmas generated at the back faces of detonating explosives (Cook’s plasmas) has a similar basis. Numerical estimates are given to justify this interpretation.
Ferroelectric epitaxial nanocrystals obtained by a self-patterning method
Authors: Szafraniak I. , Harnagea C. , Scholz R. , Bhattacharyya S. , Hesse D. , Alexe M.
Published: September 2003

Lead zirconate titanate nanoislands were obtained by a self-patterning method making use of the instability of ultrathin films during high-temperature treatments. After high-temperature annealing, the as-deposited film breaks into islands with a narrow size distribution. The single-crystal nanoislands were studied by scanning and high-resolution transmission electron microscopy, atomic force microscopy, and x-ray diffraction. They show an epitaxial relationship with the Nb-doped (001) SrTiO3 substrate. The ferroelectric switching of several individual islands was investigated by piezoresponse force microscopy.
Ultrahigh magnetic field sensitivity in laminates of TERFENOL-D and Pb(Mg1/3Nb2/3)O3–PbTiO3 crystals
Authors: Dong Shuxiang , Li Jie-Fang , Viehland D.
Published: September 2003

It has been found that laminate composites of longitudinally magnetized magnetostrictive TERFENOL-D and a transversely poled piezoelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 crystal have extremely high magnetic field sensitivity. At room temperature, an output voltage with an exceptionally good linear response to an ac magnetic field Hac was found over the range of 10−11<Hac<10−3 T.
Evidence for energy coupling from the Si–D vibration mode to the Si–Si and Si–O vibration modes at the SiO2/Si interface
Authors: Chen Zhi , Guo Jun , Ong Pangleen
Published: September 2003

In order to verify Van de Walle and Jackson’s theory on the isotope effect of the Si–H/D bonds resistant to hot-electron excitation [C. G. Van de Walle and W. B. Jackson, Appl. Phys. Lett., 69, 2441 (1996)], we measured the Si–H, Si–D, and other vibrational modes in the oxidized silicon wafers annealed in hydrogen and deuterium using Fourier-transform infrared (FTIR) spectrometry. Our FTIR data suggest that the frequency for the Si–D bending mode at the SiO2/Si interface is 490 cm−1. Our experimental data support Van de Walle and Jackson’s theory with some modification. Their theory is correct for the experiments of breaking Si–H/D bonds using scanning tunneling microscope where no oxide involves. In the SiO2/Si case, the de-excitation of the Si–D bond may be due to the energy coupling from the Si–D bending mode to two vibrational modes, i.e., Si–O TO mode and the Si–Si TO phonon mode. Van de Walle and Jackson only pointed out coupling to Si–Si TO phonon mode. The strongest coupling might happen between the Si–D mode and the Si–O TO mode. Therefore, the oxide may play a crucial role in energy dissipation of the Si–D bond in metal–oxide–semiconductor devices.
Low-field electron emission from tetrapod-like ZnO nanostructures synthesized by rapid evaporation
Authors: Wan Q. , Yu K. , Wang T. H. , Lin C. L.
Published: September 2003

Tetrapod-like zinc oxide (ZnO) nanostructures can be synthesized by rapid heating metal zinc pellet at 900 °C under air ambient. Catalyst, vacuum, and carrying gas are not necessary, and more importantly, it is a volcanic process for rapid and mass production. The turn-on field of the synthesized tetrapod-like ZnO nanostructures is found to be as low as 1.6 V/μm at the current density of 1 μA/cm2. These ZnO nanostructures are technologically useful for vacuum electron devices because they can be easily and economically synthesized and deposited on large substrates.
Analysis of bycatch in the fishery for orange roughy, Hoplostethus atlanticus, on the South Tasman Rise
Authors: Anderson Owen F. , Clark Malcolm R.
Published: September 2003

Government fisheries observers made detailed records of the catch weights of all species caught on 545 trawls between October 1997 and August 2000 in the South Tasman Rise orange roughy (Hoplostethus atlanticus) fishery. Bycatch ratios, the ratio of bycatch weight to tow duration, were derived from these data and used to make estimates of total annual bycatch for several species groups. Bycatch ratios based on tow duration were chosen over ratios based on orange roughy catch weights after comparing the coefficients of variation (c.v.) of sets of trial data. Bycatch ratios and total bycatch were estimated for three species of oreos (Oreosomatidae), corals and all other bycatch species combined, for the fishing years from 1997–1998 to 2000–2001. Total oreo bycatch dropped from about 7400 t to less than 350 t during this time. These estimates agreed well with recorded oreo landings data for three of the four years. There was a considerable bycatch of corals, with both the bycatch ratio and the total bycatch reducing during the period examined, the latter from about 1750 t to 100 t per year. The coral bycatch comprised a large number of species, but was dominated by the reef-forming stony coral Solenosmilia variabilis. Annual bycatch of all other species combined, mainly rattails (Macrouridae) and dogfishes (Squalidae), was low (13–120 t). Bycatch of this group dropped sharply in each year as the result of a combination of decreasing bycatch ratio and decreasing fishing effort.
Patterns of connectivity among populations of Cherax destructor (Decapoda : Parastacidae) in western Queensland, Australia
Authors: Hughes Jane M. , Hillyer Mia J.
Published: September 2003

Freshwater organisms are often hypothesized to reflect the hierarchical nature of stream channels in the genetic structure of their populations. However, patterns of genetic structure are also affected by the dispersal mechanism of the particular species and the nature of the river channels. In this study, the genetic structure of a freshwater crayfish, known to have the ability for terrestrial dispersal, was examined in a habitat where stream structure and elevational differences across catchment boundaries are minimal. It was found that levels of connectivity among populations in the same catchment are high, suggesting either recent or contemporary dispersal among them. In contrast, almost no sharing of haplotypes across drainage boundaries indicates limited terrestrial dispersal across them. However, nested clade analysis indicated that, historically, there has been movement between drainages. It is suggested that populations in the Cooper and Murray–Darling were isolated in the past and that, more recently, recolonization has occurred in an east–west direction from the Murray–Darling to the Bulloo and from the Bulloo to the Cooper. These movements probably occurred in wetter times when whole catchments were flooded.
Morphological studies of Ganoderma (Ganodermataceae) from the Australasian and Pacific regions
Authors: Smith Brendan J. , Sivasithamparam K.
Published: September 2003

Ganoderma, a genus of approximately 214 described species has been deemed to be in taxonomic chaos. The difficulties stem from the large numbers of synonymies, widespread misuse of names, typification problems and a paucity of reliable morphological characters. In Australia, all of these problems are represented and the genus is in need of revision. In this study six species of Ganoderma were identified among several collections. A new species, G. steyaertanum sp. nov., is described from Australian and Indonesian material. This species has been commonly mistaken for G. lucidum, a species which is probably restricted to Europe and from which G.�steyaertanum is genetically distinct. The remaining species were determined to be G. boninense, G. cupreum, G.�incrassatum (a name which has not recently featured in literature), G. australe and G. weberianum. All were verified against type material except G. australe, which is in need of neotypification as the type is lost. G. tornatum, a widely accepted synonym, may take precedence; however, we have been unable to examine the type for verification. Based on morphology, G. polymorphum was identified as a synonym of G. cupreum. On the basis of morphology and previously published rDNA sequence studies, G. microsporum was considered a synonym of G.�weberianum. A seventh species, G. colossum, has also been reported from Australia; however the specimen was not available for verification in this study.
Field swelling, shrinking, and water content change in a heavy clay soil
Authors: Kirby J. M. , Bernardi A. L. , Ringrose-Voase A. J. , Young R. , Rose H.
Published: September 2003

We measured the volumetric water content (using neutron moisture meters) and height changes (using rods fixed in the soil at different depths) of several soil layers during swelling or shrinking of a heavy clay soil in the Liverpool Plains of New South Wales under 3 treatments: (1) a sorghum–fallow–lucerne, (2) continuous lucerne, and (3) continuous fallow. Treatment 1 resulted in weak drying and shrinking (in the sorghum phase), followed by weak wetting and swelling (fallow), and then strong drying (lucerne) accompanied by shrinkage of up to about 140 mm in the top 3 m of the profile. Treatment 2 resulted in repeated wetting and drying, with repeated swelling and shrinking. The continuous fallow treatment (3) had an initially dry profile (following a lucerne crop) and we roughened (chisel ploughed) the surface to promote infiltration. This resulted in a strong wetting event with swelling of up to about 200 mm in the top 3 m of the profile. There were clear trends between water storage change and height change for the first and third treatments, but not for the continuous lucerne treatment.The relationship between water storage change and height change was consistent with a constant of proportionality (α) of 0.33, unchanging with depth. The data were also consistent with α increasing slightly in deeper soil layers. There was no evidence of α approaching 1 (which is sometimes reported in the literature for wet soil) or zero (which is often reported in drier soil and equated with residual shrinkage), nor of differences in behaviour on wetting and drying.The height change measurements permitted estimation of the true water storage changes with swelling or shrinkage taken into account. Failure to take volume change into account (i.e. of treating the neutron moisture readings as correct) led to errors in the estimated profile water storage of up to 80 mm. The apparent (uncorrected for volume change) profile moisture storages were readily corrected using a simple analysis based on the assumption of proportionality between water storage change and volume change. The analysis leads to a correction 1/(1 – αθ) (where θ is the volumetric water content). For our data the correction was about 15–20%.
Winter wheat in England and Wales, 1923–1995: what do indices of genetic diversity reveal?
Authors: Srinivasan C. S. , Thirtle Colin , Palladino Paolo
Published: September 2003

Genealogical data have been used very widely to construct indices with which to examine the contribution of plant breeding programmes to the maintenance and enhancement of genetic resources. In this paper we use such indices to examine changes in the genetic diversity of the winter wheat crop in England and Wales between 1923 and 1995. We find that, except for one period characterized by the dominance of imported varieties, the genetic diversity of the winter wheat crop has been remarkably stable. This agrees with many studies of plant breeding programmes elsewhere. However, underlying the stability of the winter wheat crop is accelerating varietal turnover without any significant diversification of the genetic resources used. Moreover, the changes we observe are more directly attributable to changes in the varietal shares of the area under winter wheat than to the genealogical relationship between the varieties sown. We argue, therefore, that while genealogical indices reflect how well plant breeders have retained and exploited the resources with which they started, these indices suffer from a critical limitation. They do not reflect the proportion of the available range of genetic resources which has been effectively utilized in the breeding programme: complex crosses of a given set of varieties can yield high indices, and yet disguise the loss (or non-utilization) of a large proportion of the available genetic diversity.
Utilization of plant genetic resources in breeding for sustainability
Authors: Humphreys M. O.
Published: September 2003

UK agriculture is undergoing significant change with reduced subsidies for food production, increasing consumer demands for food safety and traceability, and environmental concerns including climate and demographic change. The International Treaty on Plant Genetic Resources for Food and Agriculture adopted by the United Nations Food and Agriculture Organisation supports the use of genetic resources for research and breeding. Mining genetic resources for useful genetic variation is perceived as a major benefit of genebanks. However, utilization by breeders may be constrained by poor characterization of genetic resources, a widening gap between improved and unimproved material, and the disruption of well- adapted genotypes during introgression. Breeders working with grasses and forage legumes for sustainable agriculture are fortunate in the wealth of genetic variation available both within the primary species of interest and among related species. New DNA technologies allow more targeted approaches to the use of these genetic resources. Possibilities for gene transfer between related species using conventional techniques expand the available gene pools while potential use of genetic transformation extend these even further.
Dynamics of filaments: modelling the dynamics of driven microfilaments
Authors: Lowe Christopher P.
Published: September 2003

We describe a method for simulating the inertialess dynamics of a flexible filament immersed in a fluid. Typically, this regime is appropriate for filaments a few micrometres or less in size (flagella that propel micro-organisms for example). We apply the model to two systems; a filament that is wiggled at one end and planar swimming motion characteristic of simple spermatozoa. For the former we find qualitative agreement with theory. The shape is determined by a balance between bending and viscous forces and there is an optimal balance that maximizes the propulsion generated by this mechanism. Quantitatively we find less satisfactory agreement. For the spermatozoa, assuming a relatively naive bending mechanism in the form of a travelling force quadrupole wave, the model generates waveforms in very good agreement with experiment. This is only true, however, if the bending forces acting on the filament are large compared with the viscous forces. Experimental measurements of the tail stiffness imply this should not be the case. We discuss the implications of this observation in the context of the sperm's swimming mechanism.
Aspects of skeletal muscle modelling
Authors: Epstein Marcelo , Herzog Walter
Published: September 2003

The modelling of skeletal muscle raises a number of philosophical questions, particularly in the realm of the relationship between different possible levels of representation and explanation. After a brief incursion into this area, a list of desiderata is proposed as a guiding principle for the construction of a viable model, including: comprehensiveness, soundness, experimental consistency, predictive ability and refinability. Each of these principles is illustrated by means of simple examples. The presence of internal constraints, such as incompressibility, may lead to counterintuitive results. A one-panel example is exploited to advocate the use of the principle of virtual work as the ideal tool to deal with these situations. The question of stability in the descending limb of the force–length relation is addressed and a purely mechanical analogue is suggested. New experimental results confirm the assumption that fibre stiffness is positive even in the descending limb. The indeterminacy of the force–sharing problem is traditionally resolved by optimizing a, presumably, physically meaningful target function. After presenting some new results in this area, based on a separation theorem, it is suggested that a more fundamental approach to the problem is the abandoning of optimization criteria in favour of an explicit implementation of activation criteria.
Does Lowering Glutamine Synthetase Activity in Nodules Modify Nitrogen Metabolism and Growth of Lotus japonicus?
Authors: Harrison Judith , Pou de Crescenzo Marie-Anne , Sené Olivier , Hirel Bertrand
Published: September 2003

A cDNA encoding cytosolic glutamine synthetase (GS) from Lotus japonicus was fused in the antisense orientation relative to the nodule-specific LBC3 promoter of soybean (Glycine max) and introduced into L. japonicus via transformation with Agrobacterium tumefaciens. Among the 12 independent transformed lines into which the construct was introduced, some of them showed diminished levels of GS1 mRNA and lower levels of GS activity. Three of these lines were selected and their T1 progeny was further analyzed both for plant biomass production and carbon and nitrogen (N) metabolites content under symbiotic N-fixing conditions. Analysis of these plants revealed an increase in fresh weight in nodules, roots and shoots. The reduction in GS activity was found to correlate with an increase in amino acid content of the nodules, which was primarily due to an increase in asparagine content. Thus, this study supports the hypothesis that when GS becomes limiting, other enzymes (e.g. asparagine synthetase) that have the capacity to assimilate ammonium may be important in controlling the flux of reduced N in temperate legumes such as L. japonicus. Whether these alternative metabolic pathways are important in the control of plant biomass production still remains to be fully elucidated.
Nodule-Specific Modulation of Glutamine Synthetase in Transgenic Medicago truncatula Leads to Inverse Alterations in Asparagine Synthetase Expression
Authors: Carvalho Helena G. , Lopes-Cardoso Inês A. , Lima Ligia M. , Melo Paula M. , Cullimore Julie V.
Published: September 2003

Transgenic Medicago truncatula plants were produced harboring chimeric gene constructs of the glutamine synthetase (GS) cDNA clones (MtGS1a or MtGS1b) fused in sense or antisense orientation to the nodule-specific leghemoglobin promoter Mtlb1. A series of transgenic plants were obtained showing a 2- to 4-fold alteration in nodule GS activity when compared with control plants. Western and northern analyses revealed that the increased or decreased levels of GS activity correlate with the amount of cytosolic GS polypeptides and transcripts present in the nodule extracts. An analysis of the isoenzyme composition showed that the increased or decreased levels of GS activity were attributable to major changes in the homo-octameric isoenzyme GS1a. Nodules of plants transformed with antisense GS constructs showed an increase in the levels of both asparagine synthetase (AS) polypeptides and transcripts when compared with untransformed control plants, whereas the sense GS transformants showed decreased AS transcript levels but polypeptide levels similar to control plants. The polypeptide abundance of other nitrogen metabolic enzymes NADH-glutamic acid synthase and aspartic acid amino-transferase as well as those of major carbon metabolic enzymes phosphoenolpyruvate carboxylase, carbonic anhydrase, and sucrose synthase were not affected by the GS-gene manipulations. Increased levels of AS polypeptides and transcripts were also transiently observed in nodules by inhibiting GS activity with phosphinothricin. Taken together, the results presented here suggest that GS activity negatively regulates the level of AS in root nodules of M. truncatula. The potential role of AS in assimilating ammonium when GS becomes limiting is discussed.
Sodium Influx and Accumulation in Arabidopsis
Authors: Essah Pauline A. , Davenport Romola , Tester Mark
Published: September 2003

Arabidopsis is frequently used as a genetic model in plant salt tolerance studies, however, its physiological responses to salinity remain poorly characterized. This study presents a characterization of initial Na+ entry and the effects of Ca2+ on plant growth and net Na+ accumulation in saline conditions. Unidirectional Na+ influx was measured carefully using very short influx times in roots of 12-d-old seedlings. Influx showed three components with distinct sensitivities to Ca2+, diethylpyrocarbonate, and osmotic pretreatment. Pharmacological agents and known mutants were used to test the contribution of different transport pathways to Na+ uptake. Influx was stimulated by 4-aminobutyric acid and glutamic acid; was inhibited by flufenamate, quinine, and cGMP; and was insensitive to modulators of K+ and Ca2+ channels. Influx did not differ from wild type in akt1 and hkt1 insertional mutants. These data suggested that influx was mediated by several different types of nonselective cation channels. Na+ accumulation in plants grown in 50 mm NaCl was strongly reduced by increasing Ca2+ activity (from 0.05-3.0 mm), and plant survival was improved. However, plant biomass was not affected by shoot Na+ concentration, suggesting that in Arabidopsis Na+ toxicity is not dependent on shoot Na+ accumulation. These data suggest that Arabidopsis is a good model for investigation of Na+ transport, but may be of limited utility as a model for the study of Na+ toxicity.
Metabolic Profiling of Transgenic Tomato Plants Overexpressing Hexokinase Reveals That the Influence of Hexose Phosphorylation Diminishes during Fruit Development
Authors: Roessner-Tunali Ute , Hegemann Björn , Lytovchenko Anna , Carrari Fernando , Bruedigam Claudia , Granot David , Fernie Alisdair R.
Published: September 2003

We have conducted a comprehensive metabolic profiling on tomato (Lycopersicon esculentum) leaf and developing fruit tissue using a recently established gas chromatography-mass spectrometry profiling protocol alongside conventional spectrophotometric and liquid chromatographic methodologies. Applying a combination of these techniques, we were able to identify in excess of 70 small-M  r metabolites and to catalogue the metabolite composition of developing tomato fruit. In addition to comparing differences in metabolite content between source and sink tissues of the tomato plant and after the change in metabolite pool sizes through fruit development, we have assessed the influence of hexose phosphorylation through fruit development by analyzing transgenic plants constitutively overexpressing Arabidopsis hexokinase AtHXK1. Analysis of the total hexokinase activity in developing fruits revealed that both wild-type and transgenic fruits exhibit decreasing hexokinase activity with development but that the relative activity of the transgenic lines with respect to wild type increases with development. Conversely, both point-by-point and principal component analyses suggest that the metabolic phenotype of these lines becomes less distinct from wild type during development. In summary, the data presented in this paper demonstrate that the influence of hexose phosphorylation diminishes during fruit development and highlights the importance of greater temporal resolution of metabolism.
Members of the Arabidopsis-SKP1-like Gene Family Exhibit a Variety of Expression Patterns and May Play Diverse Roles in Arabidopsis
Authors: Zhao Dazhong , Ni Weimin , Feng Baomin , Han Tianfu , Petrasek Megan G. , Ma Hong
Published: September 2003

Ubiquitin-mediated proteolysis by the proteasome is a critical regulatory mechanism controlling many biological processes. In particular, SKP1, cullin/CDC53, F-box protein (SCF) complexes play important roles in selecting substrates for proteolysis by facilitating the ligation of ubiquitin to specific proteins. In plants, SCF complexes have been found to regulate auxin responses and jasmonate signaling and may be involved in several other processes, such as flower development, circadian clock, and gibberellin signaling. Although 21 Skp1-related genes, called Arabidopsis-SKP1-like (ASK), have been uncovered in the Arabidopsis genome, ASK1 is the only gene that has been analyzed genetically. As a first step toward understanding their functions, we tested for expression of 20 ASK genes using reverse transcription-polymerase chain reaction experiments. Also, we examined the expression patterns of 11 ASK genes by in situ hybridizations. The ASK genes exhibit a spectrum of expression levels and patterns, with a large subset showing expression in the flower and/or fruit. In addition, the ASK genes that have similar sequences tend to have similar expression patterns. On the basis of the expression results, we selectively suppressed the expression of a few ASK genes using RNA interference. Compared with the ask1 mutant, the strong ASK1 RNA interference (RNAi) line exhibited similar or enhanced phenotypes in both vegetative and floral development, whereas ASK11 RNAi plants had normal vegetative growth but mild defects in flower development. The diverse expression patterns and distinct defects observed in RNAi plants suggest that the ASK gene family may collectively perform a range of functions and may regulate different developmental and physiological processes.
The polycotyledon Mutant of Tomato Shows Enhanced Polar Auxin Transport
Authors: Al-Hammadi Arif S.A. , Sreelakshmi Yellamaraju , Negi Sangeeta , Siddiqi Imran , Sharma Rameshwar
Published: September 2003

The polycotyledon mutant of tomato (Lycopersicon esculentum L. cv Ailsa Craig) showed altered development during embryogenesis and during vegetative and reproductive phases. The phenotype was pleiotropic and included the formation of extra cotyledons, changes in leaf shape, increased number of flowers (indeterminacy) with abnormal floral organs, the formation of epiphyllous structures, and altered gravitropism. The earliest defects were observed at the transition from the globular to the heart stage of embryogenesis with the formation of multiple cotyledons. Epidermal cells in the mutant embryo were smaller and less expanded compared with wild type. Examination of polar auxin transport (PAT) showed a striking enhancement in the case of the mutant. Increase in PAT did not appear to be caused by a decrease in flavonoids because the mutant had normal flavonoid levels. Application of 2,3,5-triiodobenzoic acid, an inhibitor of polar transport of auxin, rescued postgermination phenotypes of young seedlings. Our analysis reveals a level of control that negatively regulates PAT in tomato and its contribution to plant development and organogenesis.
E‐opportunities of service sector SMEs: an Irish cross‐border study
Authors: Ramsey Elaine , Ibbotson Pat , Bell Jim , Gray Brendan
Published: September 2003

The Internet is causing fundamental changes in the economics of service industries as new, network‐based global e‐business models emerge, where small‐ and medium‐sized enterprises (SMEs) have been identified as key users of Internet commerce. Initially the paper contextualises the research issues via a review of the theoretical opportunities afforded firms of all sizes. Correspondingly, an examination of the practical impediments from an SME perspective suggests that, among other things, there are major hurdles for SMEs going online including strategic appreciation of the dynamics of the Web and the development of capabilities for managing the information infrastructure for e‐business. To illustrate the inherent issues, the findings of empirical research are presented. Both inductive and deductive methodological approaches were employed to investigate e‐business awareness, attitudes and activities among a sample of Irish (north and south) service sector SMEs.
A conceptualisation of the opportunities and barriers to e‐business development in the smaller firm
Authors: Fillis Ian , Johansson Ulf , Wagner Beverly
Published: September 2003

Drawing on existing research on e‐business and the smaller firm, this paper presents a review of the literature and the formulation of a conceptual framework of adopting an e‐business approach. Macro‐factors, industry sector, firm and managerial motivations and attitudes are examined, and then positioned in a conceptual framework of e‐business development in domestic and international markets. A series of research propositions are developed which go beyond the formalised, prescriptive frameworks of e‐business as presented in marketing and e‐commerce textbooks. These include the belief that those firms with a high degree of entrepreneurial orientation will be more likely to develop interests in e‐business than their conservative counterparts. Other factors include firm size, age of the manager, particular industry sector and product type. Conceptualises the tangible and intangible factors which impact upon the process of e‐business development, to present a workable framework for future qualitative and quantitative data collection.
Infant Stress and Parent Responsiveness: Regulation of Physiology and Behavior During Still‐Face and Reunion
Authors: Haley David W. , Stansbury Kathy
Published: September 2003

This study examined infant response and recovery from a social challenge and parent responses. Behavioral and physiological responses were measured from forty‐three 5‐ and 6‐month‐olds infants during a modified still‐face procedure that used an additional still‐face reunion sequence. Results confirm the hypothesis that infants of more responsive parents show more regulation than infants of less responsive parents. Infants of more responsive parents showed greater regulation of heart rate and negative affect during the final episode of the procedure than infants of less responsive parents. In addition, this procedure elicited a cortisol response (from .22 μg/dl to .31 μg/dl). Findings suggest important links between parent behavior and infant stress reactivity and regulation.
A Study of AdaBoost with Naive Bayesian Classifiers: Weakness and Improvement
Authors: Ting Kai Ming , Zheng Zijian
Published: September 2003

This article investigates boosting naive Bayesian classification. It first shows that boosting does not improve the accuracy of the naive Bayesian classifier as much as we expected in a set of natural domains. By analyzing the reason for boosting's weakness, we propose to introduce tree structures into naive Bayesian classification to improve the performance of boosting when working with naive Bayesian classification. The experimental results show that although introducing tree structures into naive Bayesian classification increases the average error of the naive Bayesian classification for individual models, boosting naive Bayesian classifiers with tree structures can achieve significantly lower average error than both the naive Bayesian classifier and boosting the naive Bayesian classifier, providing a method of successfully applying the boosting technique to naive Bayesian classification. A bias and variance analysis confirms our expectation that the naive Bayesian classifier is a stable classifier with low variance and high bias. We show that the boosted naive Bayesian classifier has a strong bias on a linear form, exactly the same as its base learner. Introducing tree structures reduces the bias and increases the variance, and this allows boosting to gain advantage.
Belief, Logic, and Partial Truth
Authors: Snow Paul
Published: September 2003

Contrary to some interpretations of “impossibility theorems,” belief models exist which are both truth‐functional and give equal credibility to all equivalent formulas. This combination of features can be useful, e.g., in case‐based reasoning. That such models exist casts doubt on theories which try to restrict the applications of belief calculi based upon the supposed incompatibility of the features. One prominent theory attempts to divorce partial truth, described as the province of fuzzy logic, from probabilistic reasoning. Nevertheless, ordinary logic and cumulative probability exactly restate the inferences of the usual fuzzy logic.
Exploring the Dimensionality of Trust in Risk Regulation
Authors: Poortinga Wouter , Pidgeon Nick F.
Published: September 2003

This article investigates possible differential levels of trust in government regulation across five different risk contexts and the relationship between a number of concepts that might be thought of as comprising distinctive “dimensions” of trust. It appeared that how people perceive government and its policies toward risk regulation was surprisingly similar for each of the five risk cases. A principal‐component analysis showed that the various trust items could best be described by two dimensions: a general trust dimension, which was concerned with a wide range of trust‐relevant aspects, such as competence, care, fairness, and openness, and a scepticism component that reflects a sceptical view regarding how risk policies are brought about and enacted. Again, the results were surprisingly similar across the five risk cases, as the same solution was found in each of the different samples. It was also examined whether value similarity has an additional value in predicting trust in risk regulation, compared to the more conventional aspects of trust. Based on the two independent trust factors that were found in this study, a typology of trust is proposed that ranges from full trust to a deep type of distrust. It is argued that for a functioning society it could well be more suitable to have critical but involved citizens in many situations.
Surface reaction of bis(tertbutylimido)bis(diethylamido)tungsten precursor on Si(100)–(2×1)
Authors: Wu Jin-Bao , Yang Yaw-wen , Lin Yi-Feng , Chiu Hsin-Tien
Published: September 2003

Thermal decomposition of a metal-organic chemical vapor deposition precursor, (t-BuN=)2W(–NEt2)2, (bis(tertbutylimido)bis(diethylamido)tungsten, on Si(100) has been studied by means of synchrotron radiation-based x-ray photoemission spectroscopy and temperature programmed desorption spectroscopy. The resultant thin films consist of tungsten metal, silicon carbides and silicon nitrides. Major desorption products originated from ligand decomposition include imine (C2H5N=CHCH3) that is derived from β-H elimination of diethylamido ligand, and isobutene (C4H8) that is generated from γ-H elimination of t-butylimido ligands. The transmetalation of the precursor leads to tungsten metal adsorption on Si(100); by contrast, tungsten nitrides, tungsten carbides and tungsten oxides are produced as the same precursor is decomposed on SiO2 surface.
Ultrathin copper aluminum and nickel aluminide protective oxidation studied with an x-ray photoelectron spectrometer
Authors: Moore J. F. , McCann M. P. , Pellin M. J. , Zinovev A. , Hryn J. N.
Published: September 2003

Oxidation in a regime where diffusion is rapid and pressures are low is addressed. Kinetic effects under these conditions are minimized and a protective oxide film of near-equilibrium composition that is a few nanometers thick may form. Ultrathin oxides have great potential for addressing the corrosion resistance of metals, since they do not always suffer stress-induced cracking upon thermal cycling, and can be reformed under high temperature, oxidizing environments. Ultrathin oxide films are also preferable to those on a thick oxide scale for electrochemical applications due to their electrical properties. To study the growth of these oxide films, we have developed a high signal x-ray photoelectron spectrometer. The instrument can measure the near-surface composition during growth under oxygen partial pressures of up to 10−5 mbar and surface temperatures up to 1300 K. Under these conditions, films grow to a level of 3 nm in 1 h. Experiments with Cu–Al alloys show rapid segregation of Al upon oxygen exposure at 875 K, whereas exposures at lower temperatures result in a mixed oxide. With a Ni–Al intermetallic, higher temperatures were needed to preferentially segregate Al. Thermal cycling followed by exposure to chlorine in the same instrument is used as a measure of the degree of corrosion resistance of the oxides in question.
Investigation of interactions between inert gases and nitrogen in direct current triode discharges
Authors: Davison A. , Avelar-Batista J. C. , Wilson A. D. , Leyland A. , Matthews A. , Fancey K. S.
Published: September 2003

Neon–nitrogen and argon–nitrogen thermionically supported dc triode discharges (typical of those used in plasma-assisted physical vapor deposition processes) have been investigated using optical emission spectroscopy. All discharges were operated with the cathode current density and voltage maintained at 0.06 mA/cm2 and −100 V. A range of nitrogen partial pressures was examined in each inert gas discharge at total pressures of 1.3 and 4.7 Pa. Spectral line intensity ratios were used to obtain information on the species within the plasma region of the discharge, from which the following effects were noted at both total pressures: (i) The N2+/N20 ratio was observed to increase significantly at low nitrogen partial pressures in the neon-based discharges; this is attributed to Penning ionization by neon metastables. (ii) The maximum in the N2+/N20 ratio and minimum in the Ne+/Ne0 ratio occurred at ∼10% nitrogen partial pressure, indicating optimum conditions for Penning ionization. (iii) For nitrogen partial pressures of less than 10%, an increase in atomic nitrogen species was observed for both inert gas discharges; this effect is attributed to the dissociation of nitrogen molecular species (both ionized and neutral) by inert gas metastables.