bluuebunny/crossref_metadata_2025 huggingface dataset:
Mutual orientation of two C60 molecules: An ab initio study
Authors: Tournus Florent , Charlier Jean-Christophe , Mélinon Patrice
Published: February 2005

The orientational dependence of the interaction between two C60 molecules is investigated using ab initio calculations. The binding energy, computed within density functional theory in the local density approximation, is substantially smaller than the one derived from the experimental heat of sublimation of fullerite, which calls into question the nature of inter-C60 bonding. According to our calculations, the experimentally observed orientation with a C60 presenting a hexagon-hexagon bond to a pentagonal face of the other C60 is not really favored. Some other configurations are very close in energy and in fact a pentagon facing a pentagon and a hexagon facing a hexagon-hexagon bond are found to be slightly more favorable situations. Our results are compared to previous ones obtained either with previous empirical intermolecular potentials or to existing ab initio studies of crystalline C60. In addition, the stacking of C60 in a crystal and in a decahedral (C60)7 cluster is discussed.
Titration of hydrophobic polyelectrolytes using Monte Carlo simulations
Authors: Ulrich Serge , Laguecir Abohachem , Stoll Serge
Published: February 2005

The conformation and titration curves of weak (or annealed) hydrophobic polyelectrolytes have been examined using Monte Carlo simulations with screened Coulomb potentials in the grand canonical ensemble. The influence of the ionic concentration pH and presence of hydrophobic interactions has been systematically investigated. A large number of conformations such as extended, pearl-necklace, cigar-shape, and collapsed structures resulting from the subtle balance of short-range hydrophobic attractive interactions and long-range electrostatic repulsive interactions between the monomers have been observed. Titration curves were calculated by adjusting the pH-pK0 values (pK0 represents the intrinsic dissociation constant of an isolated monomer) and then calculating the ionization degree α of the polyelectrolyte. Important transitions related to cascades of conformational changes were observed in the titration curves, mainly at low ionic concentration and with the presence of strong hydrophobic interactions. We demonstrated that the presence of hydrophobic interactions plays an important role in the acid-base properties of a polyelectrolyte in promoting the formation of compact conformations and hence decreasing the polyelectrolyte degree of ionization for a given pH-pK0 value.
Local-MP2 electron correlation method for nonconducting crystals
Authors: Pisani C. , Busso M. , Capecchi G. , Casassa S. , Dovesi R. , Maschio L. , Zicovich-Wilson C. , Schütz M.
Published: February 2005

Rigorous methods for the post-HF (HF—Hartree–Fock) determination of correlation corrections for crystalline solids are currently being developed following different strategies. The CRYSTAL program developed in Torino and Daresbury provides accurate HF solutions for periodic systems in a basis set of Gaussian type functions; for insulators, the occupied HF manifold can be represented as an antisymmetrized product of well localized Wannier functions. This makes possible the extension to nonconducting crystals of local correlation linear scaling On techniques as successfully and efficiently implemented in Stuttgart’s MOLPRO program. These methods exploit the fact that dynamic electron correlation effects between remote parts of a molecule (manifesting as dispersive interactions in intermolecular perturbation theory) decay as an inverse sixth power of the distance R between these fragments, that is, much more quickly than the Coulomb interactions that are treated already at the HF level. Translational symmetry then permits the crystalline problem to be reduced to one concerning a cluster around the reference zero cell. A periodic local correlation program (CRYSCOR) has been prepared along these lines, limited for the moment to the solution of second-order Møller-Plesset equations. Exploitation of point group symmetry is shown to be more important and useful than in the molecular case. The computational strategy adopted and preliminary results concerning five semiconductors with tetrahedral structure (C, Si, SiC, BN, and BeS) are presented and discussed.
Stripes of partially fluorinated alkyl chains: Dipolar Langmuir monolayers
Authors: Schneider Matthias F. , Andelman David , Tanaka Motomu
Published: February 2005

Stripelike domains of Langmuir monolayers formed by surfactants with partially fluorinated lipid anchors (F-alkyl lipids) are observed at the gas-liquid phase coexistence. The average periodicity of the stripes, measured by fluorescence microscopy, is in the micrometer range, varying between 2 and 8μm. The observed stripelike patterns are stabilized due to dipole-dipole interactions between terminal– CF3 groups. These interactions are particularly strong as compared with nonfluorinated lipids due to the low dielectric constant of the surrounding media (air). These long-range dipolar interactions tend to elongate the domains, in contrast to the line tension that tends to minimize the length of the domain boundary. This behavior should be compared with that of the lipid monolayer having alkyl chains, and which form spherical microdomains (bubbles) at the gas-liquid coexistence. The measured stripe periodicity agrees quantitatively with a theoretical model. Moreover, the reduction in line tension by adding traces (0.1mol%) of cholesterol results, as expected, in a decrease in the domain periodicity.
Operator splitting algorithm for isokinetic SLLOD molecular dynamics
Authors: Pan Guoai , Ely James F. , McCabe Clare , Isbister Dennis J.
Published: February 2005

We apply an operator splitting method to develop a simulation algorithm that has complete analytical solutions for the Gaussian thermostated SLLOD equations of motion [D. J. Evans and G. P. Morriss, Phys. Rev. A 30, 1528 (1984)] for a system under shear. This leads to a homogeneous algorithm for performing both equilibrium and nonequilibrium isokinetic molecular dynamics simulation. The resulting algorithm is computationally efficient. In particular, larger integration time steps can be used compared to simulations with regular Gaussian thermostated SLLOD equations of motion. The utility and accuracy of the algorithm are demonstrated through application to the Weeks–Chandler–Anderson fluid. Although strict conservation of the kinetic energy suppresses thermal fluctuations in the system, this algorithm does not allow simulations at lower shear rates than those normally afforded by older nonequilibrium molecular dynamics simulations.
A smooth particle-mesh Ewald algorithm for Stokes suspension simulations: The sedimentation of fibers
Authors: Saintillan David , Darve Eric , Shaqfeh Eric S. G.
Published: February 2005

Large-scale simulations of non-Brownian rigid fibers sedimenting under gravity at zero Reynolds number have been performed using a fast algorithm. The mathematical formulation follows the previous simulations by Butler and Shaqfeh [“Dynamic simulations of the inhomogeneous sedimentation of rigid fibres,” J. Fluid Mech. 468, 205 (2002)]. The motion of the fibers is described using slender-body theory, and the line distribution of point forces along their lengths is approximated by a Legendre polynomial in which only the total force, torque, and particle stresslet are retained. Periodic boundary conditions are used to simulate an infinite suspension, and both far-field hydrodynamic interactions and short-range lubrication forces are considered in all simulations. The calculation of the hydrodynamic interactions, which is typically the bottleneck for large systems with periodic boundary conditions, is accelerated using a smooth particle-mesh Ewald (SPME) algorithm previously used in molecular dynamics simulations. In SPME the slowly decaying Green’s function is split into two fast-converging sums: the first involves the distribution of point forces and accounts for the singular short-range part of the interactions, while the second is expressed in terms of the Fourier transform of the force distribution and accounts for the smooth and long-range part. Because of its smoothness, the second sum can be computed efficiently on an underlying grid using the fast Fourier transform algorithm, resulting in a significant speed-up of the calculations. Systems of up to 512 fibers were simulated on a single-processor workstation, providing a different insight into the formation, structure, and dynamics of the inhomogeneities that occur in sedimenting fiber suspensions.
Experimental studies of occupation and transit times in turbulent flows
Authors: Jørgensen J. Berg , Mann J. , Ott S. , Pécseli H. L. , Trulsen J.
Published: February 2005

The motion of passively advected particles is studied experimentally in approximately homogeneous and isotropic turbulent flows. The turbulence is generated in water by two moving grids. The simultaneous trajectories of many small passively advected, neutrally buoyant polystyrene particles are followed in time by a particle tracking technique. We estimate the probability distribution of the transit times of such particles in spherical volumes with given radius. A particle which is passively advected by the flow is selected to define the center of a reference sphere, with the transit time being defined as the difference between entrance and exit times of surrounding particles advected through this sphere by the turbulent motions. Simple scaling laws are obtained for the probability density of the transit times in terms of the basic properties of the turbulent flow and the geometry. Also other formulations of the problem have been considered, by assuming, for instance, that particle positions are uniformly distributed within the reference sphere, and then determine the statistical distribution of the time they subsequently spend inside the sphere, i.e., their occupation time. These problems have Eulerian counterparts, and they were analyzed as well. In the present formulation, we find that the results of the analysis are relevant for understanding certain details in the feeding rate of microorganisms in turbulent waters, for instance.
Importance of the gas phase role to the prediction of energetic material behavior: An experimental study
Authors: Ali A. N. , Son S. F. , Asay B. W. , Sander R. K.
Published: February 2005

Various thermal (radiative, conductive, and convective) initiation experiments are performed to demonstrate the importance of the gas phase role in combustion modeling of energetic materials (EM). A previously published condensed phase model that includes a predicted critical irradiance above which ignition is not possible is compared to experimental laser ignition results for octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and 2,4,6-trinitrotoluene (TNT). Experimental results conflict with the predicted critical irradiance concept. The failure of the model is believed to result from a misconception about the role of the gas phase in the ignition process of energetic materials. The model assumes that ignition occurs at the surface and that evolution of gases inhibits ignition. High speed video of laser ignition, oven cook-off and hot wire ignition experiments captures the ignition of HMX and TNT in the gas phase. A laser ignition gap test is performed to further evaluate the effect of gas phase laser absorption and gas phase disruption on the ignition process. Results indicate that gas phase absorption of the laser energy is probably not the primary factor governing the gas phase ignition observations. It is discovered that a critical gap between an HMX pellet and a salt window of 6mm±0.4mm exists below which ignition by CO2 laser is not possible at the tested irradiances of 29W∕cm2 and 38W∕cm2 for HMX ignition. These observations demonstrate that a significant disruption of the gas phase, in certain scenarios, will inhibit ignition, independent of any condensed phase processes. These results underscore the importance of gas phase processes and illustrate that conditions can exist where simple condensed phase models are inadequate to accurately predict the behavior of energetic materials.
Optical instrument for measurement of vaginal coating thickness by drug delivery formulations
Authors: Henderson Marcus H. , Peters Jennifer J. , Walmer David K. , Couchman Grace M. , Katz David F.
Published: February 2005

An optical device has been developed for imaging the human vaginal epithelial surfaces, and quantitatively measuring distributions of coating thickness of drug delivery formulations—such as gels—applied for prophylaxis, contraception or therapy. The device consists of a rigid endoscope contained within a 27-mm-diam hollow, polished-transparent polycarbonate tube (150mm long) with a hemispherical cap. Illumination is from a xenon arc. The device is inserted into, and remains stationary within the vagina. A custom gearing mechanism moves the endoscope relative to the tube, so that it views epithelial surfaces immediately apposing its outer surface (i.e., 150mm long by 360° azimuthal angle). Thus, with the tube fixed relative to the vagina, the endoscope sites local regions at distinct and measurable locations that span the vaginal epithelium. The returning light path is split between a video camera and photomultiplier. Excitation and emission filters in the light path enable measurement of fluorescence of the sited region. Thus, the instrument captures video images simultaneously with photometric measurement of fluorescence of each video field [∼10mm diameter; formulations are labeled with 0.1%w∕w United States Pharmacoepia (USP) injectable sodium fluorescein]. Position, time and fluorescence measurements are continuously displayed (on video) and recorded (to a computer database). The photomultiplier output is digitized to quantify fluorescence of the endoscope field of view. Quantification of the thickness of formulation coating of a surface sited by the device is achieved due to the linear relationship between thickness and fluorescence intensity for biologically relevant thin layers (of the order of 0.5mm). Summary measures of coating have been developed, focusing upon extent, location and uniformity. The device has begun to be applied in human studies of model formulations for prophylaxis against infection with HIV and other sexually transmitted pathogens.
The effect of gravity on liquid plug propagation in a two-dimensional channel
Authors: Suresh V. , Grotberg J. B.
Published: February 2005

The effect of plug propagation speed and gravity on the quasisteady motion of a liquid plug in a two-dimensional liquid-lined channel oriented at an angle α with respect to gravity is studied. The problem is motivated by the transport of liquid plugs instilled into pulmonary airways in medical treatments such as surfactant replacement therapy, drug delivery, and liquid ventilation. The capillary number Ca is assumed to be small, while the Bond number Bo is arbitrary. Using matched asymptotic expansions and lubrication theory, expressions are obtained for the thickness of the trailing films left behind by the plug and the pressure drop across it as functions of Ca, Bo, α and the thickness of the precursor films. When the Bond number is small it is found that the trailing film thickness and the flow contribution to the pressure drop scale as Ca2∕3 at leading order with coefficients that depend on Bo and α. The first correction to the film thickness is found to occur at O(Ca) compared to O(Ca4∕3) in the Bo=0 case. Asymmetry in the liquid distribution is quantified by calculating the ratio of liquid volumes above and below the centerline of the channel, VṘ. VR=1 at Bo=0, indicating a symmetric distribution, and decreases with Bo and Ca, but increases with the plug length Lp. The decrease of VR with Ca suggests that higher propagation speeds in small airways may result in less homogenous liquid distribution, which is in contrast to the expected effect in large airways. For given values of the other parameters, a maximum capillary number Cac is identified above which the plug will eventually rupture. When the Bond number becomes equal to an orientation-dependent critical value Boc, it is found that the scaling of the film thickness and pressure drop change to Ca1∕2 and Ca1∕6, respectively. It is shown that this scaling is valid for small increments of the Bond number over its critical value, Bo=Boc+BCa1∕6, but for higher Bond numbers the asymptotic approach breaks down.
Comparison of blue and green InGaN∕GaN multiple-quantum-well light-emitting diodes grown by metalorganic vapor phase epitaxy
Authors: Qi Y. D. , Liang H. , Wang D. , Lu Z. D. , Tang W. , Lau K. M.
Published: February 2005

In Ga N ∕ Ga N multiple-quantum-well (MQW) blue and green-light-emitting diodes (LEDs) were grown on sapphire substrates using metalorganic vapor phase epitaxy. High-resolution transmission microscopy shows that a much larger density of stacking faults exist in the quantum-well region of the blue LEDs than in the green LEDs. In the green LEDs, the blueshift in the electroluminescence (EL) emission energy at larger driving currents is more prominent than in the blue LEDs, which is explained by different strength of quantum-confined Stark effect as a result of different piezoelectric field intensity by different scales of strain relaxation in the blue and green MQWs. The steady broadening of the EL emission energy linewidth on the higher energy side with the increase of the driving current was observed in both blue and green LEDs, which is attributed to the band filling effect.
Highly ordered CdS nanoparticle arrays on silicon substrates and photoluminescence properties
Authors: Lei Y. , Chim W. K. , Sun H. P. , Wilde G.
Published: February 2005

Highly ordered cadmium sulphide (CdS) nanoparticle (NP) arrays were fabricated on silicon (Si) substrates using ultrathin alumina membranes as evaporation masks. The CdS NPs are polycrystalline and are composed of ultrasmall closely packed nanocrystallites. These crystallites increase in size as the duration of the CdS evaporation process increases. When the thickness of the NPs changes from about 10 to 50 nm, the size of the crystallites increases from about 5–14 to 20–40 nm. Photoluminescence measurements on the CdS NP arrays show a strong emission spectrum with two subbands that are attributed to band-edge and surface-defect emissions. The peak position and width of the band-edge emission band are closely related to the size of the crystallites in the CdS NPs.
Mechanisms of B deactivation control by F co-implantation
Authors: Cowern N. E. B. , Colombeau B. , Benson J. , Smith A. J. , Lerch W. , Paul S. , Graf T. , Cristiano F. , Hebras X. , Bolze D.
Published: February 2005

Thermal annealing after preamorphization and solid-phase epitaxy of ultrashallow B implants leads to deactivation and diffusion driven by interstitials released from end-of-range defects. F inhibits these processes by forming small clusters that trap interstitials. A competing B–F interaction causes deactivation when F and B profiles overlap. Both pathways suppress B transient enhanced diffusion.
The existence of vortices in the wakes of simulated raindrops
Authors: Saylor J. R. , Jones B. K.
Published: February 2005

Flow visualizations are presented of the wakes behind water droplets traveling at terminal velocity in a vertically directed airflow. These images, obtained by levitating water drops in a vertical wind tunnel, reveal vortices in the wake behind the drop. It has long been postulated that such wakes trigger transverse oscillations in raindrops. Although such transverse oscillations were not observed here, the images do show a canting of the oblate drop which appears to be connected to the vortex shedding process. These are the first images of simulated raindrops that visualize both the shape of the drop and the vortices in the wake immediately behind the drop.
Fabrication and optical investigation of a high-density GaN nanowire array
Authors: Wang T. , Ranalli F. , Parbrook P. J. , Airey R. , Bai J. , Rattlidge R. , Hill G.
Published: February 2005

A high-density GaN nanowire array has been successfully fabricated through self-organized nanometer-sized holes as mask appearing in InGaN layer. The self-organized nanometer-sized holes are naturally formed during InGaN epitaxial growth using metalorganic chemical vapor deposition technology by modifying growth parameters. Scanning electron microcopy and atomic force microcopy have been used to characterize them. Optical investigation was carried out by room-temperature photoluminescence, which indicated that strong emission from an n-GaN nanowire array was observed at 367 nm, the near-band edge emission wavelength for n-type GaN. The results show that excellent optical properties of the GaN nanowire array can be obtained by this technique. It is important to point out that GaN-based nanolaser or nano-light-emitting diodes with different emission wavelengths can be potentially achieved using this technology.
Directive emissions from subwavelength metamaterial-based cavities
Authors: Zhou Lei , Li Hongqiang , Qin Yaqin , Wei Zeyong , Chan C. T.
Published: February 2005

We use experiment and theory to demonstrate a mechanism for directive emissions, which involves a double-plate resonance cavity made with metamaterials. In contrast to other mechanisms employing Fabry-Pérot cavities, photonic crystals, or zero index materials, our system is significantly thinner than the working wavelength and requires a smaller lateral size. We show the physics to be governed by subwavelength resonance modes unique to such metamaterial-based cavities.
Proteome analysis of two soft-grained wheats of different processing quality: cultivar-specific proteins
Authors: Skylas D. J. , Cordwell S. J. , Craft G. , McInerney B. , Wu M. J. , Chin J. , Wrigley C. W. , Sharp P. J.
Published: February 2005

Proteome analysis was conducted on the grain of 2 closely related soft biscuit-making wheats (Bowie and Rosella cultivars) differing in processing quality. Comparisons between these wheat cultivars were carried out on total wholemeal proteins, extracts with enriched starch granule proteins, and extracts enriched with gliadin storage proteins, with the intention of characterising, identifying, and cataloguing cultivar-specific proteins that could be used for segregation purposes. Initially, 2-dimensional gel electrophoresis was carried out on total wholemeal proteins using a broad range pH 3–10 immobilised pH gradient for the first dimension. Further screening was carried out using a combination of mid to narrow range immobilised pH gradients, including pH 4–7, 5.5–6.7, 5–8, 6–9, and 6–11. Best cultivar-specific protein fractionation was provided by the pH 5–8 range. Altogether, 4 unique cultivar-specific protein spots were excised from the pH 5–8 gels and identified by means of peptide mass fingerprinting, tandem mass spectrometry, or N-terminal sequencing. Starch granule protein extracts were prepared and fractionated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A western blot was performed and probed with an anti-puroindoline-a antibody. Further to this, extracts enriched in gliadin storage proteins were isolated using 70% ethanol and analysed by 2-dimensional gel electrophoresis. The resulting gliadin protein maps showed 18 unique cultivar-specific gliadins. They were excised from the pH 6–9 gels and submitted for N-terminal amino acid sequencing. Overall, this study identified 23 proteins that could be used to distinguish between these closely related cultivars and may provide information on the molecular basis for the differences in processing exhibited by these wheats. The findings reported also contribute to a longer term objective of developing a broad and comprehensive knowledge base of commercial wheats, in regard to protein composition and their inherent processing qualities.
Foliar nitrogen applications increase the seed yield and protein content in chickpea (Cicer arietinum L.) subject to terminal drought
Authors: Palta Jairo A. , Nandwal Ajit S. , Kumari Sunita , Turner Neil C.
Published: February 2005

The effect of foliar application of isotopically labelled nitrogen (15N-urea) at 4 stages during flowering and podding on the uptake and utilisation of nitrogen by chickpea (Cicer arietinum L.) under conditions of terminal drought was investigated in a glasshouse study. Five treatments were used to investigate the effect of timing of foliar application of urea, equivalent to 30 kg N/ha, on the uptake and utilisation of nitrogen for biomass, yield, seed protein content, and seed size: foliar application at (i) first flower, (ii) 50% flowering, (iii) 50% pod set, and (iv) the end of podding, and (v) an unsprayed control treatment. Terminal drought was induced from pod set onward, resulting in a rapid development of plant water deficits (–0.14 MPa/day) and a decrease in leaf photosynthesis irrespective of the timing of foliar urea application. Foliar applications of urea at first flower and at 50% flowering, before terminal drought was induced, increased yield and seed protein content. The increase in yield resulted from an increase in the number of pods with more than one seed rather than from increased pod number per plant or increased seed size, indicating greater seed survival under terminal drought. Also, the increase in the seed protein content resulted from increased nitrogen availability for seed filling. Foliar application of urea during flowering, before terminal drought was induced, resulted in 20% more biomass at maturity, suggesting that growth prior to the development of water shortage increased the carbon resources for sustained seed filling under conditions of terminal drought. Foliar applications of urea at 50% pod set and at the end of podding did not affect the yield or seed protein content, primarily because the uptake of nitrogen was limited by the leaf senescence that occurred with the development of terminal drought. The results indicate the potential to increase yields of chickpea by application of foliar nitrogen near flowering in environments in which terminal droughts reduce yield.
Prediction of aspects of neutral detergent fibre digestion of forages by chemical composition and near infrared reflectance spectroscopy
Authors: Andrés S. , Giráldez F. J. , González J. S. , Peláez R. , Prieto N. , Calleja A.
Published: February 2005

Sixty-two herbage samples, harvested in natural meadows located in the mountains of León (north-west Spain), and characterised by a diverse botanical composition and different stages of maturity of the plants, were used to evaluate the ability of chemical composition and near infrared (NIR) spectroscopy to predict in vitro digestibility and in sacco degradability of the neutral detergent fibre (NDF) fraction. In vitro digestibility was performed as described by the Goering and Van Soest procedure. Three dry Holstein-Friesian cows fitted with a rumen cannula were used to incubate the herbage samples. A Bran+Luebbe InfraAlyzer 500 spectrophotometer was used to obtain the NIR spectra corresponding to the 62 original herbage samples. Prediction equations for the estimation of in vitro digestibility and in sacco degradability parameters of the NDF fraction were generated using NIR spectra or chemical data as independent variables. The results showed that the in vitro digestibility and kinetic parameters of degradation of the NDF fraction could not be predicted accurately, probably as a consequence of the errors corresponding to the reference methods. In contrast, these errors did not greatly affect the extent of disappearance of the NDF fraction at later times, so the accuracy of prediction of these parameters was higher, especially when NIR spectra were used as independent variables. This is probably due to the close relationship that the parameters showed with the chemical data, since this kind of information, together with some physical characteristics of the samples, is included in the NIR spectra.
The hot and the cold: unravelling the variable response of plant respiration to temperature
Authors: Atkin Owen K. , Bruhn Dan , Hurry Vaughan M. , Tjoelker Mark G.
Published: February 2005

When predicting the effects of climate change, global carbon circulation models that include a positive feedback effect of climate warming on the carbon cycle often assume that (1) plant respiration increases exponentially with temperature (with a constant Q10) and (2) that there is no acclimation of respiration to long-term changes in temperature. In this review, we show that these two assumptions are incorrect. While Q10 does not respond systematically to elevated atmospheric CO2 concentrations, other factors such as temperature, light, and water availability all have the potential to influence the temperature sensitivity of respiratory CO2 efflux. Roots and leaves can also differ in their Q10 values, as can upper and lower canopy leaves. The consequences of such variable Q10 values need to be fully explored in carbon modelling. Here, we consider the extent of variability in the degree of thermal acclimation of respiration, and discuss in detail the biochemical mechanisms underpinning this variability; the response of respiration to long-term changes in temperature is highly dependent on the effect of temperature on plant development, and on interactive effects of temperature and other abiotic factors (e.g. irradiance, drought and nutrient availability). Rather than acclimating to the daily mean temperature, recent studies suggest that other components of the daily temperature regime can be important (e.g. daily minimum and / or night temperature). In some cases, acclimation may simply reflect a passive response to changes in respiratory substrate availability, whereas in others acclimation may be critical in helping plants grow and survive at contrasting temperatures. We also consider the impact of acclimation on the balance between respiration and photosynthesis; although environmental factors such as water availability can alter the balance between these two processes, the available data suggests that temperature-mediated differences in dark leaf respiration are closely linked to concomitant differences in leaf photosynthesis. We conclude by highlighting the need for a greater process-based understanding of thermal acclimation of respiration if we are to successfully predict future ecosystem CO2 fluxes and potential feedbacks on atmospheric CO2 concentrations.
Plant phosphorus status has a limited influence on the concentration of phosphorus-mobilising carboxylates in the rhizosphere of chickpea
Authors: Wouterlood Madeleine , Lambers Hans , Veneklaas Erik J.
Published: February 2005

Two experiments were conducted to investigate whether carboxylate exudation by chickpea (Cicer arietinum L.) is a response to phosphorus (P) deficiency or a constitutive trait. The effect of P supply on carboxylate concentrations in the plant and in the rhizosphere of chickpea cultivar Heera was studied in a sand culture. Plants were grown in pots supplied with 200 mL of solution containing 0–500 μm P every 3 d. Malonate was the main carboxylate exuded, and the main carboxylate in roots; shoots contained mainly citrate and malate. Contrary to what has been reported for other species, carboxylate concentrations in the rhizosphere decreased only slightly at high P supply, but they were still substantial. The effect of P supply on the rate of exudation was studied in a split-root sand culture. Root systems were split into two pots, one root half received no P and the other half received 200 mL of solution containing 0–500 μm P. The rhizosphere of both root halves contained similar concentrations of carboxylates, even when the plants received a different supply of P. Our results indicate that carboxylate exudation is determined by internal P rather than external factors. The fact that chickpea roots always exude carboxylates indicates that exudation in this species is largely constitutive.
Evidence for Na+/Ca2+ Exchanger 1 Association with Caveolin‐1 and ‐2 in C6 Glioma Cells
Authors: Cha Seok Ho , Shin Sun Young , Jung Sang Yong , Kim Yun Tai , Park Yong Joo , Kwak Jin‐Oh , Kim Hyun‐Woo , Suh Chang Kook
Published: February 2005

The purpose of this study is to understand the interaction of Na+‐Ca2+ exchanger (NCX1), that is one of the essential regulators of Ca2+ homeostasis, with caveolin (Cav)‐1 and Cav‐2 in Cav‐3 null cell (rat C6 glioma cell). Both mRNA and protein expression of NCX1, Cav‐1 and Cav‐2 was observed, but no expression of mRNA and protein of Cav‐3 were observed in C6 glioma cells. In isolated caveolae‐enriched membrane fraction, the NCX1, Cav‐1 and Cav‐2 proteins localized in same fractions. The experiment of immuno‐precipitation showed complex formation between the NCX1 and Cavs. Confocal microscopy also supported co‐localization of NCX1 and Cavs at the plasma membrane. Functionally, sodium‐free induced forward mode of NCX1 attenuated by Cav‐1 antisense ODN. When treated cells with Cav‐2 antisense ODN, both reverse and forward mode of NCX1 was attenuated. From these results, in the Cav‐3 lacking cells, the function of NCX1 might be regulated by binding with Cavs. Considering the decrement of NCX1 activity by antisense ODNs, caveolins may play an important role in diverse of pathophysiological process of NCX1‐related disorders in the body.
IUBMB Life, 56: 621‐627, 2004
Insulin Regulation of Fatty Acid Synthase Gene Transcription: Roles of USF and SREBP‐1c
Authors: Griffin Michael J. , Sul Hei Sook
Published: February 2005

The transcriptional regulation of lipogenesis is a highly coordinated process occurring in concert with transcriptional as well as post‐transcriptional regulation of enzymes involved in glycolysis and gluconeogenesis. Fatty acid synthase (FAS) plays a central role in de novo lipogenesis by converting acetyl‐CoA and malonyl‐CoA into the final end product, palmitate, which can subsequently be esterified into triacylglycerols and then stored in adipose tissue. Ultimately, this helps to prevent buildup of excess glucose in other types of cells and tissues, the effects of which can be readily observed in the pathophysiology of disease states such as Type‐II diabetes and obesity. Thus, elucidating the transcriptional mechanisms of lipogenic enzyme genes is important for understanding the normal regulation of lipogenesis and ultimately the dysregulation that may occur in certain metabolic disease. In this review, we discuss advances in our understanding of the regulation of lipogenesis at the genetic level, with a special emphasis on the common cis‐ and trans‐acting factors involved in regulation of FAS. Two transcription factors, Upstream Stimulatory Factor (USF) and Sterol Regulatory Element Binding Protein‐1c (SREBP‐1c), seem to play a dominant and possibly cooperative role in regulating FAS transcription.
IUBMB Life, 56: 595‐600, 2004
Long-range cooperative binding of kinesin to a microtubule in the presence of ATP
Authors: Muto Etsuko , Sakai Hiroyuki , Kaseda Kuniyoshi
Published: February 2005

Interaction of kinesin-coated latex beads with a single microtubule (MT) was directly observed by fluorescence microscopy. In the presence of ATP, binding of a kinesin bead to the MT facilitated the subsequent binding of other kinesin beads to an adjacent region on the MT that extended for micrometers in length. This cooperative binding was not observed in the presence of ADP or 5′-adenylylimidodiphosphate (AMP-PNP), where binding along the MT was random. Cooperative binding also was induced by an engineered, heterodimeric kinesin, WT/E236A, that could hydrolyze ATP, yet remained fixed on the MT in the presence of ATP. Relative to the stationary WT/E236A kinesin on a MT, wild-type kinesin bound preferentially in close proximity, but was biased to the plus-end direction. These results suggest that kinesin binding and ATP hydrolysis may cause a long-range state transition in the MT, increasing its affinity for kinesin toward its plus end. Thus, our study highlights the active involvement of MTs in kinesin motility.
Functional Interactions Between A' Helices in the C-linker of Open CNG Channels
Authors: Hua Li , Gordon Sharona E.
Published: February 2005

Cyclic nucleotide-gated (CNG) channels are nonselective cation channels that are activated by the direct binding of the cyclic nucleotides cAMP and cGMP. The region linking the last membrane-spanning region (S6) to the cyclic nucleotide binding domain in the COOH terminus, termed the C-linker, has been shown to play an important role in coupling cyclic nucleotide binding to opening of the pore. In this study, we explored the intersubunit proximity between the A' helices of the C-linker regions of CNGA1 in functional channels using site-specific cysteine substitution. We found that intersubunit disulfide bonds can be formed between the A' helices in open channels, and that inducing disulfide bonds in most of the studied constructs resulted in potentiation of channel activation. This suggests that the A' helices of the C-linker regions are in close proximity when the channel is in the open state. Our finding is not compatible with a homology model of the CNGA1 C-linker made from the recently published X-ray crystallographic structure of the hyperpolarization-activated, cyclic nucleotide-modulated (HCN) channel COOH terminus, and leads us to suggest that the C-linker region depicted in the crystal structure may represent the structure of the closed state. The opening conformational change would then involve a movement of the A' helices from a position parallel to the axis of the membrane to one perpendicular to the axis of the membrane.
Anosov automorphisms on compact nilmanifolds associated with graphs
Authors: Dani S. , Mainkar Meera
Published: February 2005

We associate with each graph

(
S
,
E
)

(S,E)

a

2
2

-step simply connected nilpotent Lie group

N
N

and a lattice

Γ
\Gamma

in

N
N

. We determine the group of Lie automorphisms of

N
N

and apply the result to describe a necessary and sufficient condition, in terms of the graph, for the compact nilmanifold

N

/

Γ

N/\Gamma

to admit an Anosov automorphism. Using the criterion we obtain new examples of compact nilmanifolds admitting Anosov automorphisms, and conclude that for every

n
≥
17

n\geq 17

there exist a

n
n

-dimensional

2
2

-step simply connected nilpotent Lie group

N
N

which is indecomposable (not a direct product of lower dimensional nilpotent Lie groups), and a lattice

Γ
\Gamma

in

N
N

such that

N

/

Γ

N/\Gamma

admits an Anosov automorphism; we give also a lower bound on the number of mutually nonisomorphic Lie groups

N
N

of a given dimension, satisfying the condition. Necessary and sufficient conditions are also described for a compact nilmanifold as above to admit ergodic automorphisms.
Clustering in coagulation-fragmentation processes, random combinatorial structures and additive number systems: Asymptotic formulae and limiting laws
Authors: Freiman Gregory , Granovsky Boris
Published: February 2005

We develop a unified approach to the problem of clustering in the three different fields of applications indicated in the title of the paper, in the case when the parametric function of the models is regularly varying with positive exponent. The approach is based on Khintchine’s probabilistic method that grew out of the Darwin-Fowler method in statistical physics. Our main result is the derivation of asymptotic formulae for the distribution of the largest and the smallest clusters (= components), as the total size of a structure (= number of particles) goes to infinity. We discover that

n

1

l
+
1

n^{\frac {1}{l+1}}

is the threshold for the limiting distribution of the largest cluster. As a by-product of our study, we prove the independence of the numbers of groups of fixed sizes, as

n
→
∞
.

n\to \infty .

This is in accordance with the general principle of asymptotic independence of sites in mean-field models. The latter principle is commonly accepted in statistical physics, but not rigorously proved.
Investigating team work in the Egyptian context
Authors: El‐Kot Ghada , Leat Mike
Published: February 2005

Purpose

The aim is to explore in the Egyptian context the incidence and pervasiveness of teamworking, the types of teams in use, and to gather information on some of the factors perceived by researchers in the West to be influential in determining team effectiveness.

Design/methodology/approach

This paper reports and discusses a preliminary inquiry in a sample of 20 manufacturing and service organisations in Egypt. The research was conducted by way of face‐to‐face semi‐structured interviews with between three and five managers in each of the organisations. Comparisons are drawn with much of the western literature and further research needs are identified.

Findings

This initial survey has provided evidence of the utilisation of teamworking in a sample of employing organisations in Egypt, which in several respects appears to reflect trends and developments in the more developed economies of the West.

Research limitations/implications

In this survey only some of the factors identified as influencing team effectiveness were investigated and further research is required to examine in more detail the relevance of the various models of team effectiveness devised by researchers in the western context.

Practical implications

The research was exploratory and is the precursor to a wider and deeper study concerning team effectiveness in the Egyptian context.

Originality/value

The study reported is initial and exploratory in nature and, as far as the authors are aware, the first study of teamworking in Egypt.
Cultural lag: a relevant framework for social justice
Authors: Brinkman Richard L. , Brinkman June E.
Published: February 2005

Purpose

This paper aims to show the interrelation and relevancy of the concept and theory of cultural lag to social justice. The conception of social justice, though wide in scope, is applied in this paper to the limited domain of equality of opportunity and fairness with respect to income distribution.Design/methodology/approach – The methodology of this paper is holistic and interdisciplinary, and interrelates the social and the economic in the overall dynamics of general culture evolution.Findings – The “inverted U‐curve hypothesis” of Simon Kuznets implies that a greater equality of income distribution would be forthcoming in an economy characterized by a mature phase of modern economic growth. Empirical evidence demonstrates that such a movement toward greater equality is subject to question. The American experience of the 1920s and the period from 1973 to the present offers evidence to question the U‐curve hypothesis. Contrary to expectations, during these periods income distribution became more unequal. These periods, indicative of maladjustment, are used to demonstrate and serve as examples of cultural lags. The concept and theory of cultural lag exposes the need for prerequisite institutional adjustment. It consequently appears that the American institutional structure, currently directing the economy toward a policy orientation of laissez‐faire and the resulting increased inequality of income distribution, is anachronistic to a modern industrial society oriented toward the goal of social justice.Originality/value – Relevant to the quest of social justice.
An Estimator for Treatment Comparisons among Survivors in Randomized Trials
Authors: Hayden Douglas , Pauler Donna K. , Schoenfeld David
Published: February 2005

Summary In clinical trials of advanced‐stage disease it is often of interest to perform treatment comparisons for endpoints which are defined only for survivors. Examples include time on ventilation in ventilation studies, change in quality of life in health‐related quality‐of‐life studies, and duration of response to therapy in therapeutic trials. Randomized treatment comparisons for these endpoints cannot be performed because the outcomes are only defined in the nonrandomly selected subgroup of survivors. We propose a new evaluation of the survivor average causal effect (SACE) for treatment comparisons of this nature. We provide an estimator of SACE in the presence of no unmeasured confounders, a nontestable assumption, which identifies SACE. We also outline a sensitivity analysis for exploring robustness of conclusions to deviations from this assumption. We apply this method to duration of ventilation in a clinical trial of acute respiratory distress syndrome.
Two‐Dimensional Dose Finding in Discrete Dose Space
Authors: Wang Kai , Ivanova Anastasia
Published: February 2005

Summary The objective of a Phase I trial with two agents is to find a set of maximum‐tolerated dose combinations that yield a prespecified toxicity rate. In this article, we consider the case where several doses of one agent are fixed and the goal is to find the maximum‐tolerated dose of the other agent to be used in combination with each of the doses of agent one. We propose a Bayesian design that uses a parsimonious working model for the dose–toxicity relationship. We show that the new design is more effective in identifying the maximum‐tolerated combinations than one‐dimensional designs applied at each dose level of one of the agents.
Closure Procedures for Monotone Bi‐Factorial Dose–Response Designs
Authors: Hellmich M. , Lehmacher W.
Published: February 2005

SummaryTwo goals of multiple‐dose factorial trials are (i) demonstrating improved effectiveness of a fixed combination over each of its components as well as (ii) identifying a safe and effective dose range. The authors address both goals though with focus on the second by closure procedures that guarantee strong control of the familywise error rate. Two different families of null hypotheses are investigated for bi‐factorial dose–response designs that are monotone with respect to the matrix partial order. One is suitable to find the minimum effective dose(s) and the other one is large enough to identify the highest effective dose step(s). Likelihood ratio tests and appropriate multiple contrast tests are applied to an unbalanced clinical trial example taken fromHung(2000,Statistics in Medicine19,2079–2087). Full computer code written in theRlanguage is available from the Internet.
Survival Model Predictive Accuracy and ROC Curves
Authors: Heagerty Patrick J. , Zheng Yingye
Published: February 2005

SummaryThe predictive accuracy of a survival model can be summarized using extensions of the proportion of variation explained by the model, orR2, commonly used for continuous response models, or using extensions of sensitivity and specificity, which are commonly used for binary response models. In this article we propose new time‐dependent accuracy summaries based on time‐specific versions of sensitivity and specificity calculated over risk sets. We connect the accuracy summaries to a previously proposed global concordance measure, which is a variant of Kendall's tau. In addition, we show how standard Cox regression output can be used to obtain estimates of time‐dependent sensitivity and specificity, and time‐dependent receiver operating characteristic (ROC) curves. Semiparametric estimation methods appropriate for both proportional and nonproportional hazards data are introduced, evaluated in simulations, and illustrated using two familiar survival data sets.