bluuebunny/crossref_metadata_2025 huggingface dataset:
Anisotropic thermoelectric properties in layered cobaltite AxCoO2 (A=Sr and Ca) thin films
Authors: Kanno Tsutomu , Yotsuhashi Satoshi , Adachi Hideaki
Published: July 2004

We have fabricated epitaxial thin films of layered cobaltite AxCoO2 (A=Sr and Ca) on sapphire substrates by rf magnetron sputtering. The grown phase in the AxCoO2 films was found to be a monoclinic β-phase of primitive layered cobaltites and the epitaxial orientation of the film could be controlled by the surface plane of the substrates. The resistivity parallel to the CoO2 layers ρ‖ for the β-SrxCoO2 is as low as 2mΩcm at room temperature and shows metallic behavior. The ratio of perpendicular resistivity ρ⊥ to ρ‖ increases from 20 at room temperature to 90 at 3K. More isotropic nature was observed in the Seebeck coefficient. Parallel Seebeck coefficients S‖ of AxCoO2 are approximately 60μV∕K at room temperature and the perpendicular S⊥ are about half of S‖.
Micropatterning of metal films coated on polymer surfaces with epoxy mold and its application to organic field effect transistor fabrication
Authors: Wang Zhe , Xing Rubo , Zhang Jian , Yuan Jianfeng , Yu Xinhong , Han Yanchun
Published: July 2004

In this letter, a simple and versatile approach to micropatterning a metal film, which is evaporated on a Si substrate coated with polymer, is demonstrated by the use of a prepatterned epoxy mold. The polymer interlayer between the metal and the Si substrate is found important for the high quality pattern. When the metal–polymer–Si sandwich structure is heated with the temperature below Tm but above Tg of the polymer, the plastic deformation of the polymer film occurs under sufficiently high pressure applied. It causes the metal to crack locally or weaken along the pattern edges. Further heating while applying a lower pressure results in the formation of an intimate junction between the epoxy stamp and the metal film. Under these conditions the epoxy cures further, ensuring adhesion between the stamp and the film. The lift-off process works because the adhesion between the epoxy and the metal film is stronger than that between the metal film and the polymer. A polymer field effect transistor is fabricated in order to demonstrate potential applications of this micropatterning approach.
Study of surface acoustic phonon modes in relaxor Pb(Mg1∕3Nb2∕3)O3
Authors: Sivasubramanian V. , Kesavamoorthy R. , Sastry V. S. , Subramanian V.
Published: July 2004

Surface acoustic phonon modes in pelletized polycrystalline Pb(Mg1∕3Nb2∕3)O3 are investigated in the frequency range from 5to40cm−1 at various temperatures from 25to550°C. These spectra support the hypothesis of the core-shell nanoclusters with 1:1 ordered, negatively charged nanocore surrounded by the charge compensating positively charged disordered nanoshell. These surface acoustic modes exist even up to 550°C revealing the existence of the charged core-shell nanoclusters which is well beyond the dissolution temperature of the polar clusters in the material.
Field emission of carbon nanotubes grown on carbon cloth
Authors: Jo S. H. , Wang D. Z. , Huang J. Y. , Li W. Z. , Kempa K. , Ren Z. F.
Published: July 2004

Field emission from carbon nanotubes grown on carbon cloth has been studied. An extremely low electric field of less than 0.4V∕μm is required to reach an emission current density of 1mA∕cm2. This ultralow operating electric field of carbon nanotubes grown on carbon cloth is mainly due to a very high field enhancement factor of 1.882×104, which is the result of geometrical configuration of the carbon nanotubes and the substrate. In addition to the field enhancement, the highly disordered microstructure of carbon nanotubes grown on carbon cloth plays an important role to field emission. This unexpected result indicates that the roughness of the substrates on which carbon nanotubes grow is very important. This result also brings us significantly closer to practical applications such as highly efficient lamps, field emission displays, micro vacuum electron sources, etc.
Finite size effects in stress analysis of interconnect structures
Authors: Noyan I. C. , Murray Conal E. , Chey Jay S. , Goldsmith Charles C.
Published: July 2004

Conventional formulations of thermal stress evolution in interconnect structures usually ignore the interface integrity between the various levels. In this letter we present thermal and residual stress versus temperature data from simple copper thin-film structures on silicon. The results indicate that interconnection models which assume fully elastic behavior and perfectly bonded interfaces may yield inaccurate predictions of the thermo-mechanical response for feature sizes smaller than 10μm.
Rapidly solidified (FePt)70P30 alloy with high coercivity
Authors: Kündig A. A. , Abe N. , Ohnuma M. , Ohkubo T. , Mamiya H. , Hono K.
Published: July 2004

The alloy Fe35Pt35P30, whose composition is close to a ternary eutectic, was rapidly solidified by melt spinning and the ribbon exhibited a high coercivity, exceeding 20kOe after annealing. The alloy was mainly composed of L10 ordered FePt and PtP2 with an average grain size of about 50nm. In the as-cast state, the alloy was comprised of about 20-nm-diam FePt and PtP2 grains supersaturated with P and Fe, respectively, and the coercivity was only 150Oe. The high coercivity obtained following annealing is discussed on the basis of the microstructural observations.
Chiral and quantum size effects of single-wall carbon nanotubes on field emission
Authors: Liang Shi-Dong , Huang N. Y. , Deng S. Z. , Xu N. S.
Published: July 2004

The emission current of a single-wall carbon nanotube (SWNT) in field emission is studied by the tunneling theory with the tight-binding approach. The emission current is almost independent of the chiral angle of SWNT in low fields, but increases with increase of chiral angles in very high fields. We found a room-temperature quantum size effect of SWNT on field emission. As the diameters of SWNTs increase, the current densities decrease for metallic tubes, but increase for semiconducting tubes. When the diameters of SWNTs are larger than 2nm the current densities of metallic and semiconducting tubes are very close. These chiral and quantum size effects are originated from the energy band structure of nanotubes.
Evaluation of the discrete energy levels of individual ZnO nanorodsingle-quantum-well structures using near-field ultraviolet photoluminescence spectroscopy
Authors: Yatsui T. , Lim J. , Ohtsu M. , An S. J. , Yi G.-C.
Published: July 2004

Spatially and spectrally resolved photoluminescence imaging of individual ZnO∕ZnMgO nanorod single-quantum-well structures (SQWs) with a spatial resolution of 55nm was performed using the optical near-field technique with a metallized UV fiber probe. Using excitation power density-dependent photoluminescence spectra of a ZnO∕ZnMgO SQW nanorod, we observed the discrete energy levels in a ZnO quantum-well layer.
Photovoltage characterization of CuAlO2 crystallites
Authors: Dittrich Th. , Dloczik L. , Guminskaya T. , Lux-Steiner M. Ch. , Grigorieva N. , Urban I.
Published: July 2004

The delafossite phase of CuAlO2 has been prepared by ion exchange reaction at 475°C. The samples were characterized by x-ray diffraction, transmission electron microscopy, electron diffraction, transient and spectral photovoltage (PV), and diffuse reflectance spectroscopy. The produced CuAlO2 crystallites are p-type and of high electronic quality, i.e., no electronic transitions induced by deep states in the forbidden gap have been observed by PV. The temperature dependence of the optical band gap of CuAlO2 was measured between 80 and 600K. The band gap of CuAlO2 approximated to 0K amounts to 3.61eV. The quenching of the PV signal is thermally activated with an activation energy of 1.8eV.
Reduction of the number of electrons emitted backwardsin back-gated devices for field emission: A theoretical study
Authors: Mammana V. P. , Fonseca L. R. C.
Published: July 2004

The use of back-gated geometry (BGG) for field emission devices promises improved robustness, lower power consumption, and simpler manufacturing process. The BGG is a configuration in which the cathode is positioned between anode and gate, different from conventional approaches. Using a cylinder∕plane model to represent rows of cathode lines and the back-gate it is demonstrated that this geometry combined with an appropriate effective work-function modulation along the cathode surface can reduce the amount of electrons emitted backwards.
Evidence from atomistic simulations of fluctuation electron microscopyfor preferred local orientations in amorphous silicon
Authors: Khare S. V. , Nakhmanson S. M. , Voyles P. M. , Keblinski P. , Abelson J. R.
Published: July 2004

Simulations from a family of atomistic structural models for unhydrogenated amorphous silicon suggest that fluctuation electron microscopy experiments have observed orientational order of paracrystalline grains in amorphous silicon. This order may consist of correlations in the orientation of nearby paracrystalline grains or anisotropy in the grain shape. This observation makes a natural connection to the known growth modes of microcrystalline silicon and may be useful for other materials systems.
Pulsed inductively coupled plasmas as a method to recoup uniformity: Three-dimensional modeling study
Authors: Subramonium Pramod , Kushner Mark J.
Published: July 2004

High plasma density sources such as inductively plasmas (ICPs) are commonly used for microelectronics fabrication. Design constraints often result in systems which have asymmetric gas pumping which can in turn produce azimuthal nonuniformities in plasma properties. These asymmetries are reinforced by a positive feedback between nonuniformities in conductivity and power deposition. In this letter, we discuss computational results from a three-dimensional model for pulsed operation of ICPs sustained in argon as a means to recoup azimuthal symmetry of plasma properties which may result from asymmetric pumping. We found that azimuthally asymmetric plasma properties produced by continuous operation gradually become more uniform during pulsed operation due to the interruption of the positive feedback and allowing interpulse diffusion to smooth asymmetries.
Deformation behavior of ion-irradiated polyimide
Authors: Kucheyev S. O. , Felter T. E. , Anthamatten M. , Bradby J. E.
Published: July 2004

We study nanoindentation hardness, Young’s modulus, and tensile strength of polyimide (Kapton H) films bombarded with MeV light ions in the predominantly electronic stopping power regime. Results show that, for all the ion irradiation conditions studied, bombardment increases the hardness and Young’s modulus and decreases the tensile strength. These changes depend close to linearly on ion fluence and superlinearly (with a power-law exponent factor of ∼1.5) on electronic energy loss. Physical mechanisms of radiation-induced changes to mechanical properties of polyimide are discussed.
Self-assembled three-dimensional conducting network of single-wall carbon nanotubes
Authors: Blanchet Graciela B. , Subramoney Shekhar , Bailey R. K. , Jaycox G. D. , Nuckolls C.
Published: July 2004

We described here the self-assembling of a three-dimensional array of single-wall nanotubes (SWNTs). The distinctive choice of materials allowed for the self-assembly of SWNTs with low resistance conducting polymer links into a conducting network that when embedded into an insulating host shows no disruption of the conduction path. The ability to control network formation independently of the electrical properties of the host drastically changes the design of these conducting organic networks. Thus, enabling the tailoring of their electrical properties while addressing issues of film processability relevant for their application as printable conductors in organic electronic applications. These networks provide opportunities for applications in micro- and nanoelectronics.
Efficient bottom cathodes for organic light-emitting devices
Authors: Liu Jie , Duggal Anil R. , Shiang Joseph J. , Heller Christian M.
Published: July 2004

Bilayers of aluminum and an alkali fluoride are well-known top cathode contacts for organic light-emitting devices but have never been successfully applied as bottom contacts. We describe a bilayer bottom cathode contact for organic electronic devices based on reversing the well-known top cathode structure such that the aluminum, rather than the alkali fluoride, contacts the organic material. Electron-only devices were fabricated showing enhanced electron injection from this bottom contact. Kelvin probe, x-ray photoelectron spectroscopy experiments, and thermodynamic calculations suggest that the enhancement results from n doping of the organic material by dissociated alkali metals.
Gallium concentration dependence of room-temperature near-band-edge luminescence in n-type ZnO:Ga
Authors: Makino T. , Segawa Y. , Yoshida S. , Tsukazaki A. , Ohtomo A. , Kawasaki M.
Published: July 2004

We investigated the optical properties of epitaxial n-type ZnO films grown on lattice-matched ScAlMgO4 substrates. As the Ga doping concentration increased up to 6×1020cm−3, the absorption edge showed a systematic blueshift, consistent with the Burstein–Moss effect. A bright near-band-edge photoluminescence (PL) could be observed even at room temperature, the intensity of which increased monotonically as the doping concentration was increased except for the highest doping level. It indicates that nonradiative transitions dominate at a low doping density. Both a Stokes shift and broadening in the PL band are monotonically increasing functions of donor concentration, which was explained in terms of potential fluctuations caused by the random distribution of donor impurities.
Improved performance of 1.3μm multilayer InAs quantum-dot lasers using a high-growth-temperature GaAs spacer layer
Authors: Liu H. Y. , Sellers I. R. , Badcock T. J. , Mowbray D. J. , Skolnick M. S. , Groom K. M. , Gutiérrez M. , Hopkinson M. , Ng J. S. , David J. P. R. , Beanland R.
Published: July 2004

The use of a high-growth-temperature GaAs spacer layer is demonstrated to significantly improve the performance of 1.3μm multilayer self-assembled InAs∕InGaAs dot-in-a-well lasers. The high-growth-temperature spacer layer inhibits threading dislocation formation, resulting in enhanced electrical and optical characteristics. Incorporation of these spacer layers allows the fabrication of multilayer quantum-dot devices emitting above 1.3μm, with extremely low room-temperature threshold current densities and with operation up to 105°C.
Tailoring magnetic properties of core∕shell nanoparticles
Authors: Zeng Hao , Sun Shouheng , Li J. , Wang Z. L. , Liu J. P.
Published: July 2004

Bimagnetic FePt∕MFe2O4(M=Fe,Co) core∕shell nanoparticles are synthesized via high-temperature solution phase coating of 3.5nm FePt core with MFe2O4 shell. The thickness of the shell is controlled from 0.5 to 3nm. An assembly of the core∕shell nanoparticles shows a smooth magnetization transition under an external field, indicating effective exchange coupling between the FePt core and the oxide shell. The coercivity of the FePt∕Fe3O4 particles depends on the volume ratio of the hard and soft phases, consistent with previous theoretical predictions. These bimagnetic core∕shell nanoparticles represent a class of nanostructured magnetic materials with their properties tunable by varying the chemical composition and thickness of the coating materials.
Disorder and Urbach energy in hydrogenated amorphous carbon: A phenomenological model
Authors: Fanchini G. , Tagliaferro A.
Published: July 2004

We develop a phenomenological model describing the structural and topological effects of the disorder in hydrogenated amorphous carbons (a-C:H), through the analysis of the Raman G-peak width and the optical absorption spectra, providing information on the densities of electronic π ad π* states (πDOS). We show that the Urbach energy is not related to topological disorder but to the Gaussian width (σπ) of the πDOS, peaked at ±Eπ energies above∕below the Fermi level. σπ, on its turn, is not related in a straightforward manner to the disorder. The disorder is better represented by the σπ∕Eπ ratio, expressing the disorder-induced narrowing of the Tauc optical gap.
Increase of free carrier lifetime in nonpolar a-plane GaN grown by epitaxial lateral overgrowth
Authors: Juršènas S. , Kuokštis E. , Miasojedovas S. , Kurilčik G. , Žukauskas A. , Chen C. Q. , Yang J. W. , Adivarahan V. , Asif Khan M.
Published: July 2004

Carrier recombination dynamics in epitaxial a-plane GaN and fully coalesced epitaxial laterally overgrown (ELOG) a-plane GaN films has been studied by means of time-resolved photoluminescence under high photoexcitation. The results were compared with conventional c-plane GaN films grown under similar conditions. In a-plane GaN epilayers, the total efficiency of electron-hole plasma spontaneous luminescence decreases 20 times, whereas the luminescence decay time reduces from τLU=42 to τLU⩽10ps in comparison with c-plane GaN films. Meanwhile, an essential increase in total emission efficiency (by more than two orders of magnitude) and an increase of the decay time up to τLU=430ps have been observed for an ELOG a-plane sample in comparison with a-plane GaN films. This confirms a significant reduction of the nonradiative recombination rate for nonequilibrium carriers. Assuming a saturation of the nonradiative deep-level transitions, the room-temperature free-carrier lifetime of τ=910ps for ELOG a-plane GaN sample was obtained, which indicates on an excellent quality of the a-plane ELOG GaN films.
Lithium iodate nanocrystals in Laponite matrixfor nonlinear optical applications
Authors: Teyssier Jérémie , Dantec Ronan Le , Galez Christine , Mugnier Yannick , Bouillot Jacques , Plenet Jean-Claude
Published: July 2004

A Laponite clay-based lithium iodate nanocomposite have been synthesized for nonlinear optical applications. After addition of lithium iodate aqueous solution to a colloidal suspension of Laponite JS, thin layers are elaborated from this sol using dip-coating technique. After drying and heat treatments between 150 and 220°C, LiIO3 crystallizes in the matrix with nanometer size. As a result of their strong dipolar moment, the LiIO3 crystals can be orientated under an external electric field during nucleation. Planar waveguides have been elaborated on glass substrates and studied using m-lines spectroscopy. The experimental nonlinear optical response has been compared to predictions of a model and an effective nonlinear coefficient deff=1.4pm∕V has been measured.
Improved characteristics of organic light-emitting devicesby surface modification of nickel-doped indium tin oxide anode
Authors: Hsu Ching-Ming , Wu Wen-Tuan
Published: July 2004

This letter presents the optoelectrical performance of an organic light-emitting diode (OLED) through the elevation of indium tin oxide (ITO) anode work function by Ni co-sputter surface doping and additional O2 plasma treatment. The turn-on voltage of OLED devices can be reduced by 2.3V for Ni atomic concentration greater than 1.8% and by 2.7V for the additional O2 plasma treatment. Devices with Ni(2.6%)-doped and O2 plasma treated ITO anodes perform the highest luminance efficiency (0.91lm∕W), three times larger than undoped ITO (0.31lm∕W) at 250cd∕m2.
Background charge fluctuation in a GaAs quantum dot device
Authors: Jung S. W. , Fujisawa T. , Hirayama Y. , Jeong Y. H.
Published: July 2004

We investigate background charge fluctuation in a GaAs quantum dot device by measuring 1∕f noise in the single-electron tunneling current through the dot. The current noise is understood as fluctuations of the confinement potential and tunneling barriers. The estimated potential fluctuation increases almost linearly with temperature, which is consistent with a simple model of the 1∕f noise. We find that the fluctuation increases very slightly when electrons are injected into excited states of the quantum dot.
Real-time three-dimensional optoacoustic imaging using an acoustic lens system
Authors: Niederhauser J. J. , Jaeger M. , Frenz M.
Published: July 2004

In medical optoacoustics (photoacoustics), absorbing structures, such as blood vessels, hidden inside scattering media are illuminated with short laser pulses resulting in the generation of thermoelastic pressure transients. This initial three-dimensional (3D) acoustic pressure distribution, which exactly resembles the absorption distribution, was imaged into a water container with a 4f acoustic lens system. An optical dark-field stereo imaging system using a 30ns flash illumination light was used to capture a snapshot of the pressure-induced refraction index changes in the water container at a predetermined time after the original laser pulse. The imaging system works at 20Hz frame rate and was designed toward a theoretical resolution of 50μm. The proposed method directly provides 3D images of absorbing structures without the need of computational reconstruction algorithms.
Characterizing quantum-dot blinking using noise power spectra
Authors: Pelton Matthew , Grier David G. , Guyot-Sionnest Philippe
Published: July 2004

Fluctuations in the fluorescence from macroscopic ensembles of colloidal semiconductor quantum dots have the spectral form of 1∕f noise. The measured power spectral density reflects the fluorescence intermittency of individual dots with power-law distributions of “on” and “off” times, and can thus serve as a simple method for characterizing such blinking behavior.
The role of photochemical quenching and antioxidants in photoprotection of Deschampsia antarctica
Authors: Pérez-Torres Eduardo , García Andrea , Dinamarca Jorge , Alberdi Miren , Gutiérrez Ana , Gidekel Manuel , Ivanov Alexander G. , Hüner Norman P. A. , Corcuera Luis J. , Bravo LeónA.
Published: July 2004

Deschampsia antarctica Desv. (Poaceae) is the only grass that grows in the maritime Antarctic. Constant low temperatures and episodes of high light are typical conditions during the growing season at this latitude. These factors enhance the formation of active oxygen species and may cause photoinhibition. Therefore, an efficient mechanism of energy dissipation and / or scavenging of reactive oxygen species (ROS) would contribute to survival in this harsh environment. In this paper, non-acclimated and cold-acclimated D. antarctica were subjected to high light and / or low temperature for 24 h. The contribution of non-photochemical dissipation of excitation light energy and the activities of detoxifying enzymes in the development of resistance to chilling induced photoinhibition were studied by monitoring PSII fluorescence, total soluble antioxidants, and pigments contents and measuring variations in activity of superoxide dismutase (SOD; EC 1.15.1.1), ascorbate peroxidase (APX; EC 1.11.1.11), and glutathione reductase (GR; EC 1.6.4.2). The photochemical efficiency of PSII, measured as Fv / F m, and the yield of PSII electron transport (ΦPSII) both decreased under high light and low temperatures. In contrast, photochemical quenching (qP) in both non-acclimated and cold-acclimated plants remained relatively constant (approximately 0.8) in high-light-treated plants. Unexpectedly, qP was lower (0.55) in cold-acclimated plants exposed to 4°C and low light intensity. Activity of SOD in cold-acclimated plants treated with high light at low temperature showed a sharp peak 2–4 h after the beginning of the experiment. In cold-acclimated plants APX remained high with all treatments. Activity of GR decreased in cold-acclimated plants. Compared with other plants, D. antarctica exhibited high levels of SOD and APX activity. Pigment analyses show that the xanthophyll cycle is operative in this plant. We propose that photochemical quenching and particularly the high level of antioxidants help D. antarctica to resist photoinhibitory conditions. The relatively high antioxidant capacity of D. antarctica may be a determinant for its survival in the harsh Antarctic environment.
Corrigendum to: The relative limitation of photosynthesis by mesophyll conductance in co-occurring species in a temperate rainforest dominated by the conifer Dacrydium cupressinum
Authors: Lucia Evan H. De , Clearwater Michael J. , Whitehead David
Published: July 2004

The capacity to conduct CO2 from the intercellar spaces in leaves to the site of fixation (mesophyll conductance, gm) may pose a significant limitation to photosynthesis. Dacrydium cupressinum Sol. ex Lamb. (rimu), a native conifer of New Zealand, and other members of the Podocarpaceae evolved during the Jurassic when the partial pressure of CO2 exceeded 200 Pa. This species has low rates of photosynthesis and high levels of leaf nitrogen, which have led to the hypothesis that low gm restricts photosynthesis. Mesophyll conductance was estimated from gas-exchange and fluorescence measurements for this and other co-occurring tree species [Prumnopitys ferruginea D.�Don (miro), Weinmannia racemosa L.f. (kāmahi), Meterosideros umbellata Cav. (rata)]. Pinus radiata D. Don (radiata pine) and Phaseolus vulgaris L. (bean) were included to provide comparisons with a rapidly growing tree and herbaceous plant with relatively high photosynthetic rates. Mesophyll conductance was not statistically different among indigenous tree species but was lowest for D. cupressinum. This species also had the lowest ratio of mesophyll to stomatal conductance, gm / gst and was the only species where the decline in partial pressure of CO2 was greater from the intercellular air space to the site of fixation (16.3 Pa) than between the bulk air and the intercellular spaces (8.8 Pa), providing support for the hypotheses that low gm limits photosynthesis in this species. As a group, conifers had marginally lower gm and gm / gst ratio than angiosperms, but this difference was strongly influenced by the high values for Phaseolus vulgaris. That co-occurring members of the Podocarpaceae operated differently suggests that low gm may reflect a response to evolutionary pressures other than high atmospheric CO2 partial pressure.
Corrigendum to: Leaf water use efficiency differs between Eucalyptus seedlings from contrasting rainfall environments
Authors: Thomas Dane S. , Searson Matthew J. , Conway Jann P. , Montagu Kelvin D.
Published: July 2004

This study investigates the putative role of thicker leaves in enhancing photosynthetic capacity and water-use efficiency (WUE) of Eucalyptus species native to xeric environments. Three Eucalyptus species, Eucalyptus grandis Hill. (ex Maiden), E. sideroxylon Cunn. (ex Woolls) and E. occidentalis (Endl.), were grown under well-watered or water-limited conditions in a single compartment of a temperature-controlled glasshouse. Eucalyptus grandis is native to a mesic environment while E. sideroxylon and E. occidentalis are native to xeric environments. Leaves of E. sideroxylon and E. occidentalis were thicker and contained more nitrogen (N) on a leaf-area basis than E. grandis. Leaf gas-exchange measurements indicated that the photosynthetic capacity of E. sideroxylon and E.�occidentalis was greater than E. grandis and that stomatal conductance and WUE were negatively correlated. Whole-plant, gas-exchange and carbon-isotope measurements showed that E. sideroxylon and E. occidentalis had lower WUE than E. grandis under both well-watered and water-limited conditions. However, there was no difference in N-use efficiency between species. We suggest that stomatal conductance and leaf N content are functionally linked in these seedlings and conclude that thick leaves can, in some conditions, result in low WUE.
Do mature shade leaves of tropical tree seedlings acclimate to high sunlight and UV radiation?
Authors: Krause G. Heinrich , Grube Esther , Koroleva Olga Y. , Barth Carina , Winter Klaus
Published: July 2004

Seedlings of neotropical forest trees grown in low light were exposed to 0.5–9 h d–1 direct sunlight, for up to 3 months, to test the capability of mature shade leaves to acclimate to full solar visible and UV radiation. Photosynthetic pigments and the antioxidant, ascorbate, were analysed in leaves of two pioneer and two late-succession species. Seedlings of one or two of these species were used to assess further acclimative responses. Sun-exposure for 0.5 or 1 h d–1 resulted in strongly decreased α-carotene and increased β-carotene and lutein levels. The pool size of xanthophyll-cycle pigments (sum of viola-, anthera- and zeaxanthin) was increased and their turnover was enhanced. These changes were associated with an increase in the capacity of non-photochemical fluorescence quenching and its ‘energy-dependent’ component, qE, and with reduced susceptibility to photoinhibition of PSII. Prolonged exposure to full direct sunlight (approximately 4 or 9 h d–1) resulted in a marked decrease of chlorophyll a + b content and increase in chlorophyll a / b ratios and the pool of xanthophyll-cycle pigments (based on chlorophyll), leading to extremely high zeaxanthin levels during high-light periods. Contents of ascorbate and UV-B-absorbing substances were substantially increased. PSI activity exhibited a response to full sunlight that is characteristic of sun leaves. Rates of net photosynthetic CO2 assimilation under saturating light were increased. The data show that mature shade leaves of seedlings of both early- and late-succession tree species can substantially acclimate to full-sunlight conditions by employing similar physiological mechanisms.
Analysis of wound-induced gene expression in Nicotiana species with contrasting alkaloid profiles
Authors: Sinclair Steven J. , Johnson Richard , Hamill John D.
Published: July 2004

We determined the capacity of three Nicotiana (Solanaceae) species with very different alkaloid profiles (Nicotiana sylvestris Speg & Comes, Nicotiana alata Link & Otto and Nicotiana glauca Grah.) to increase their alkaloid contents in both leaf and root tissues following foliage damage. We also investigated the transcriptional responses of genes encoding enzymes important for alkaloid biosynthesis, namely quinolinate phosphoribosyltransferase (QPT), putrescine N-methyltransferase (PMT), ornithine decarboxylase (ODC) and the putative alkaloid biosynthetic gene A622. In response to wounding of foliage in the well studied ‘model’ species N. sylvestris, a rise, approximately 2-fold, in leaf nicotine levels was observed several days after a 4–5-fold increase in the transcript levels of all genes in the roots. In contrast, leaf tissues of the ornamental tobacco N. alata showed very low levels of any pyridine alkaloid, even when analysed 1 week after wounding, correlating with a general lack of transcript abundance representing any of these genes in leaves or roots following foliage damage. However, addition of methyl jasmonate to cultured roots of N. alata did produce elevated levels of nicotine and anatabine raising the possibility that components of the leaf–root wound signalling system in N. alata are different from those in N. sylvestris. Wounding of the tree tobacco N. glauca, was followed by a 2-fold increase in anabasine levels several days later. This increase followed a large rise in transcript levels of ODC, QPT and A622, though not PMT, in wounded leaves, but not in non-wounded leaves or roots. These data support the hypothesis that N. glauca is able to produce increased anabasine levels following wounding in its foliage, setting it apart from N. sylvestris where induced alkaloid production takes place in roots. We discuss the possibility that increased transcript levels detected by ODC and A622 probes play important roles in anabasine synthesis in N. glauca.
Quantification of stress adaptation by laser-induced fluorescence spectroscopy of plants exposed to engine exhaust emission and drought
Authors: Subhash Narayanan , Mohanan Changatharayil N. , Mallia Rupananda J. , Muralidharan Vadekkeveetil
Published: July 2004

The effects of drought and petrol engine exhaust pollutants, such as SO2 and NO2 and suspended particulate matter (SPM), on the photosynthetic activity of colocasia [Colocasia esculenta (L.) Schott], kacholam (Kaempferia galanga L.) and tapioca (Manihot esculenta Crantz) plants were studied from in vivo laser-induced chlorophyll fluorescence (LICF) spectra. An open-top chamber (OTC) of 2.5 m diameter and 3 m height incorporating an air-filtering unit was developed for this study. Plants grown inside the OTC were exposed to exhaust emissions from a two-stroke Birla Yamaha genset for 10 d, while a control group was maintained outside. Gaseous pollutants and SPM present inside the OTC during the exposure period were measured with a high-volume air sampler. The steady-state LICF spectra of the control and treated plants were recorded in the 650–750-nm region. Fluorescence induction kinetics (Kautsky effect) was also recorded during the stress period from dark-adapted intact plant leaves at the chlorophyll bands of 685 and 730 nm. The vitality indexes (Rfd-685 and Rfd-730) and stress adaptation index (Ap) derived from the induction kinetics were utilised along with the chlorophyll fluorescence intensity ratio (F685 /  F730) for evaluation of stress-induced changes in plants.
It has been observed that F685 /  F730 ratio increased for all plants inside the OTC whereas the Rfd-685, Rfd-730 and Ap values showed a downward trend with increasing pollution stress. As compared to colocasia and tapioca, kacholam plants showed higher resistance to exhaust emission and water stress as well as better capacity to regain its photosynthetic functioning on removal of the stress. Results of this study demonstrate the capability of stress adaptation index for early quantification of the functional impairment of photosynthetic apparatus in different species of plants due to air pollution and drought stresses.
Natural variation in rice starch synthase IIa affects enzyme and starch properties
Authors: Umemoto Takayuki , Aoki Noriaki , Lin Hongxuan , Nakamura Yasunori , Inouchi Naoyoshi , Sato Youichiro , Yano Masahiro , Hirabayashi Hideyuki , Maruyama Sachio
Published: July 2004

The natural variation in starch synthase IIa (SSIIa) of rice (Oryza sativa L.) was characterised using near-isogenic lines (NILs). SSIIa is a candidate for the alk gene regulating the alkali disintegration of rice grains, since both genes are genetically mapped at the same position on chromosome 6 and related to starch properties. In this study, we report that the alkali-susceptible cultivar Nipponbare lacked SSIIa activity in endosperm. However, the activity was detected with NILs having the alk allele of alkali-tolerant Kasalath. SSIIa protein was present even in Nipponbare endosperm, but it was not associated with starch granules at the milky stage of endosperm. Three single-nucleotide polymorphisms (SNPs) predicting amino acid substitutions existed between the cDNA sequences of SSIIa of Nipponbare and Kasalath were genotyped with 65 rice cultivars and four wild relatives of cultivated rice. The results obtained explain the potential importance of two of the amino acid residues for starch association of rice SSIIa. An analysis of the chain-length distribution of β-limit dextrin of amylopectin showed that without SSIIa activity, the relative number of A-chains (the short chains without branches) increased and that of B1-chains (the short chains with branches) decreased. This suggests that, given the SSIIa defect, short A-chains could not reach a sufficient length for branching enzymes to act on them to produce B1-chains.
Regulation of sucrose-phosphate synthase in wheat (Triticum aestivum) leaves
Authors: Trevanion Stephen J. , Castleden C. Kate , Foyer Christine H. , Furbank Robert T. , Quick W. Paul , Lunn John E.
Published: July 2004

The regulation of sucrose-phosphate synthase (SPS, E.C. 2.4.1.14), a key enzyme of sucrose synthesis, was investigated in wheat (Triticum aestivum L.) leaves. Wheat SPS was activated in the light, with an increased affinity for its substrates and the activator glucose-6-phosphate, reduced sensitivity to inhibition by Pi, but no change in maximum catalytic activity. Based on these properties, assays to measure the total activity and activation state of the enzyme were established and validated using several different wheat cultivars, grown under different environmental conditions. As found in previous studies on other species, e.g. spinach, activation appeared to be linked to the prevailing rate of photosynthesis rather than light per se. Long-term exposure to higher light levels increased total SPS activity in the leaves, and some experiments indicated that this response could occur within 1 h of exposure of low-light-grown plants to high light. However, activation of pre-existing enzyme was a more common short-term response to high light. Wheat, like many important cereal species, stores a large amount of sucrose in its leaves. In contrast with spinach, which stores more starch in its leaves, accumulation of sucrose in wheat leaves did not lead to inactivation of SPS or inhibition of sucrose synthesis. In conclusion, the mechanisms linking the rates of sucrose synthesis and photosynthetic CO2 fixation in wheat leaves appear to be similar to those in other species, but the mechanisms involved in short-term feedback inhibition of sucrose synthesis by sucrose, found in starch-storing species, are lacking in wheat.
The educative impact of health care treatment on malarial prevention behavior for the poor in Guinea, West Africa
Authors: McFadden Daniel L. , Sunkara Vasu
Published: July 2004

We analyze the malarial health behavior of rural populations by using data from the 1999 Demographic and Health Survey for Guinea, West Africa. We find that prior formal health care treatment is associated with heightened malaria prevention behaviors for the poorest uneducated populations in this rural cohort. Individuals from this subgroup that report no history of malarial infection and exclude themselves from health care treatment further appear to be misdiagnosing the disease at a substantial level. We conjecture that the use of formal health care options provides informational exposure to the clinical aspects of malarial pathogenesis. For individuals steeped in the most severe poverty, this exposure appears to have a particularly robust educative effect. The health behavioral dynamics we observe here have putative extensions for regional health policy as well with other infectious diseases, such as HIV/AIDS.
Reinitiation involving upstream ORFs regulates
ATF4
mRNA translation in mammalian cells
Authors: Vattem Krishna M. , Wek Ronald C.
Published: July 2004

During cellular stresses, phosphorylation of eukaryotic initiation factor-2 (eIF2) elicits gene expression designed to ameliorate the underlying cellular disturbance. Central to this stress response is the transcriptional regulator activating transcription factor, ATF4. Here we describe the mechanism regulating ATF4 expression involving the differential contribution of two upstream ORFs (uORFs) in the 5′ leader of the mouse
ATF4
mRNA. The 5′ proximal uORF1 is a positive-acting element that facilitates ribosome scanning and reinitiation at downstream coding regions in the
ATF4
mRNA. When eIF2-GTP is abundant in nonstressed cells, ribosomes scanning downstream of uORF1 reinitiate at the next coding region, uORF2, an inhibitory element that blocks
ATF4
expression. During stress conditions, phosphorylation of eIF2 and the accompanying reduction in the levels of eIF2-GTP increase the time required for the scanning ribosomes to become competent to reinitiate translation. This delayed reinitiation allows for ribosomes to scan through the inhibitory uORF2 and instead reinitiate at the
ATF4
-coding region. Increased expression of
ATF4
would contribute to the expression of genes involved in remediation of cellular stress damage. These results suggest that the mechanism of translation reinitiation involving uORFs is conserved from yeast to mammals.
Toward the synthesis of the carbacylic
ansa
antibiotic kendomycin
Authors: Mulzer Johann , Pichlmair Stefan , Green Martin P. , Marques Maria M. B. , Martin Harry J.
Published: July 2004

The convergent synthesis of a benzofuran analog of the carbacyclic
ansa
compound kendomycin has been achieved by assembling three major fragments by means of epoxide opening and directed
ortho
lithiation. The crucial tetrahydropyran ring was formed by a highly stereoselective cationic cyclization. Analysis of all synthesized tetrahydropyran-arene compounds reveals a hindered sp
2
-sp
3
rotation, which results in rotational isomers or atropisomers affecting macrocyclization reactions. The latter could only be achieved by means of Horner–Wadsworth–Emmons olefination.
G protein-coupled receptors:In silicodrug discovery in 3D
Authors: Becker Oren M. , Marantz Yael , Shacham Sharon , Inbal Boaz , Heifetz Alexander , Kalid Ori , Bar-Haim Shay , Warshaviak Dora , Fichman Merav , Noiman Silvia
Published: July 2004

The application of structure-basedin silicomethods to drug discovery is still considered a major challenge, especially when the x-ray structure of the target protein is unknown. Such is the case with human G protein-coupled receptors (GPCRs), one of the most important families of drug targets, where in the absence of x-ray structures, one has to rely onin silico3D models. We report repeated success in usingab initio in silicoGPCR models, generated by thepredictmethod, for blindin silicoscreening when applied to a set of five different GPCR drug targets. More than 100,000 compounds were typically screenedin silicofor each target, leading to a selection of <100 “virtual hit” compounds to be tested in the lab.In vitrobinding assays of the selected compounds confirm high hit rates, of 12–21% (full dose–response curves,Ki< 5 μM). In most cases, the best hit was a novel compound (New Chemical Entity) in the 1- to 100-nM range, with very promising pharmacological properties, as measured by a variety ofin vitroandin vivoassays. These assays validated the quality of the hits as lead compounds for drug discovery. The results demonstrate the usefulness and robustness ofab initio in silico3D models and ofin silicoscreening for GPCR drug discovery.
Nanometer-localized multiple single-molecule fluorescence microscopy
Authors: Qu Xiaohui , Wu David , Mets Laurens , Scherer Norbert F.
Published: July 2004

Fitting the image of a single molecule to the point spread function of an optical system greatly improves the precision with which single molecules can be located. Centroid localization with nanometer precision has been achieved when a sufficient number of photons are collected. However, if multiple single molecules reside within a diffraction-limited spot, this localization approach does not work. This paper demonstrates nanometer-localized multiple single-molecule (NALMS) fluorescence microscopy by using both centroid localization and photobleaching of the single fluorophores. Short duplex DNA strands are used as nanoscale “rulers” to validate the NALMS microscopy approach. Nanometer accuracy is demonstrated for two to five single molecules within a diffraction-limited area. NALMS microscopy will greatly facilitate single-molecule study of biological systems because it covers the gap between fluorescence resonance energy transfer-based (<10 nm) and diffraction-limited microscopy (>100 nm) measurements of the distance between two fluorophores. Application of NALMS microscopy to DNA mapping with <10-nm (i.e., 30-base) resolution is demonstrated.
A naphthyridine carboxamide provides evidence for discordant resistance between mechanistically identical inhibitors of HIV-1 integrase
Authors: Hazuda Daria J. , Anthony Neville J. , Gomez Robert P. , Jolly Samson M. , Wai John S. , Zhuang Linghang , Fisher Thorsten E. , Embrey Mark , Guare James P. , Egbertson Melissa S. , Vacca Joseph P. , Huff Joel R. , Felock Peter J. , Witmer Marc V. , Stillmock Kara A. , Danovich Robert , Grobler Jay , Miller Michael D. , Espeseth Amy S. , Jin Lixia , Chen I-Wu , Lin Jiunn H. , Kassahun Kelem , Ellis Joan D. , Wong Bradley K. , Xu Wei , Pearson Paul G. , Schleif William A. , Cortese Riccardo , Emini Emilio , Summa Vincenzo , Holloway M. Katharine , Young Steven D.
Published: July 2004

The increasing incidence of resistance to current HIV-1 therapy underscores the need to develop antiretroviral agents with new mechanisms of action. Integrase, one of three viral enzymes essential for HIV-1 replication, presents an important yet unexploited opportunity for drug development. We describe here the identification and characterization of L-870,810, a small-molecule inhibitor of HIV-1 integrase with potent antiviral activity in cell culture and good pharmacokinetic properties. L-870,810 is an inhibitor with an 8-hydroxy-(1,6)-naphthyridine-7-carboxamide pharmacophore. The compound inhibits HIV-1 integrase-mediated strand transfer, and its antiviral activity
in vitro
is a direct consequence of this ascribed effect on integration. L-870,810 is mechanistically identical to previously described inhibitors from the diketo acid series; however, viruses selected for resistance to L-870,810 contain mutations (integrase residues 72, 121, and 125) that uniquely confer resistance to the naphthyridine. Conversely, mutations associated with resistance to the diketo acid do not engender naphthyridine resistance. Importantly, the mutations associated with resistance to each of these inhibitors map to distinct regions within the integrase active site. Therefore, we propose a model of the two inhibitors that is consistent with this observation and suggests specific interactions with discrete binding sites for each ligand. These studies provide a structural basis and rationale for developing integrase inhibitors with the potential for unique and nonoverlapping resistance profiles.
Carbohydrate mimicry between human ganglioside GM1 and
Campylobacter jejuni
lipooligosaccharide causes Guillain–Barré syndrome
Authors: Yuki Nobuhiro , Susuki Keiichiro , Koga Michiaki , Nishimoto Yukihiro , Odaka Masaaki , Hirata Koichi , Taguchi Kyoji , Miyatake Tadashi , Furukawa Koichi , Kobata Tetsuji , Yamada Mitsunori
Published: July 2004

Molecular mimicry between microbial and self-components is postulated as the mechanism that accounts for the antigen and tissue specificity of immune responses in postinfectious autoimmune diseases. Little direct evidence exists, and research in this area has focused principally on T cell-mediated, antipeptide responses, rather than on humoral responses to carbohydrate structures. Guillain–Barré syndrome, the most frequent cause of acute neuromuscular paralysis, occurs 1–2 wk after various infections, in particular,
Campylobacter jejuni
enteritis. Carbohydrate mimicry [Galβ1–3GalNAcβ1–4(NeuAcα2–3)Galβ1-] between the bacterial lipooligosaccharide and human GM1 ganglioside is seen as having relevance to the pathogenesis of Guillain–Barré syndrome, and conclusive evidence is reported here. On sensitization with
C. jejuni
lipooligosaccharide, rabbits developed anti-GM1 IgG antibody and flaccid limb weakness. Paralyzed rabbits had pathological changes in their peripheral nerves identical with those present in Guillain–Barré syndrome. Immunization of mice with the lipooligosaccharide generated a mAb that reacted with GM1 and bound to human peripheral nerves. The mAb and anti-GM1 IgG from patients with Guillain–Barré syndrome did not induce paralysis but blocked muscle action potentials in a muscle–spinal cord coculture, indicating that anti-GM1 antibody can cause muscle weakness. These findings show that carbohydrate mimicry is an important cause of autoimmune neuropathy.