bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of charge transport in mercaptosuccinic acid-passivated gold clusters
Authors: Nair A. Sreekumaran , Kimura Keisaku
Published: November 2008

Investigation of electric charge transport in well-dried thin films of mercaptosuccinic acid-protected gold clusters having different cluster core sizes by a four-probe methodology revealed a novel behavior of metalliclike to semiconductor crossover with an increase in temperature. The systems were found comprising of minor metallic and major insulating networks. At low temperatures, the monolayer-protected clusters (MPCs) were found to show a metalliclike nature with a linear increase in resistivity with an increase in temperature. The temperature coefficient of resistivity decreases and approaches that of bulk gold with an increase in the size of the cluster cores of the MPCs. This behavior was correlated with the phonon softening mechanism to the electron scattering and was explained by a simple model with a spherical layer lattice vibration. High temperature region was marked by a sharp decrease in resistivity due to thermally activated nearest neighbor electron hopping process, which follows either Arrhenius or Abeles activation models. We believe that this is the first report showing a maximum in the resistivity of any MPC with temperature as also describing the effect of phonon softening on temperature coefficient of resistivity from charge transport measurements.
Sea-swell interaction as a mechanism for the generation of freak waves
Authors: Regev A. , Agnon Y. , Stiassnie M. , Gramstad O.
Published: November 2008

The probability of freak waves in an inhomogeneous ocean is studied by integration of Alber’s equation. The special phase structure of the inhomogeneous disturbance, required for instability, is provided by bound waves, generated by the quadratic interaction of the stochastic sea with a deterministic, long swell. The probability of freak waves higher than twice the significant wave height increases by a factor of up to 20 compared to the classical value given by Rayleigh’s distribution. The probability of exceptionally high freak waves, with height larger than three times the significant wave height, is shown to increase some 30 000-fold compared to that given by the Rayleigh distribution, which renders their encounter feasible.
Experimental evidence of O–H—S hydrogen bonding in supersonic jet
Authors: Biswal Himansu S. , Chakraborty Shamik , Wategaonkar Sanjay
Published: November 2008

Experimental evidence is presented for the O–H—S hydrogen bonding in the complexes of simple model compounds of methionine (dimethyl sulphide) and tyrosine (phenol, p-cresol, and 2-naphthol). The complexes were formed in the supersonic jet and were detected using resonantly enhanced multiphoton ionization spectroscopy. In all the complexes, the band origins for the S1-S0 electronic transition were redshifted relative to that of their respective monomers. The resonant ion depletion IR spectra of all the complexes show redshifts of 123–140 cm−1 in the O–H stretching frequency, indicating that the OH group acts as the hydrogen bond donor and sulfur as an acceptor. The density functional theory calculations also predict the stable structures in support of this and predict the redshifted O–H stretching frequency in the complex. The atoms-in-molecules and natural bond orbital calculations confirm the O–H—S hydrogen bonding interaction. The significant finding of this study is that the magnitudes of redshifts in the O–H stretch in the O–H—S hydrogen bonded complexes reported here are comparable to those reported for the O–H—O hydrogen bonded complexes where H2O acts as the H-bond acceptor, which suggests that the OH–S interaction is perhaps as strong as the OH–O interaction. To the best of our knowledge, this is the first such report on the O–H—S hydrogen bonded complexes.
Eigenvalue branches of the perturbed Maxwell operator M+λD in a gap of σ(M)
Authors: Miao Dong
Published: November 2008

The propagation of guided waves in photonic crystal fibers (PCFs) is studied. A PCF can be regarded as a perfectly two dimensional photonic crystal with a line defect along the axial direction. This problem can be treated as an eigenvalue problem for a family of noncompact self-adjoint operators. Under the assumption that the background spectrum has a gap, we prove that a line defect can create an eigenvalue of any given fixed value in the gap, provided that the defect is strong enough. Based on a decoupling of regions in R2 by means of Dirichlet and Neumann boundaries, then using the trace ideal estimates, we study asymptotic distribution of eigenvalues and bounds on the number of eigenvalue branches. In particular, we show that if the defect is weak enough, no eigenvalues can be created inside the gap.
Transport and bistable kinetics of a Brownian particle in a nonequilibrium environment
Authors: Chaudhuri Jyotipratim Ray , Banik Suman Kumar , Chattopadhyay Sudip , Chaudhury Pinaki
Published: November 2008

A system reservoir model, where the associated reservoir is modulated by an external colored random force, is proposed to study the transport of an overdamped Brownian particle in a periodic potential. We then derive the analytical expression for the average velocity, mobility, and diffusion rate. The bistable kinetics and escape rate from a metastable state in the overdamped region are studied consequently. By numerical simulation we then demonstrate that our analytical escape rate is in good agreement with that of the numerical result.
Stability and multiple bifurcations of a damped harmonic oscillator with delayed feedback near zero eigenvalue singularity
Authors: Song Yongli , Zhang Tonghua , Tadé Moses O.
Published: November 2008

We investigate the dynamics of a damped harmonic oscillator with delayed feedback near zero eigenvalue singularity. We perform a linearized stability analysis and multiple bifurcations of the zero solution of the system near zero eigenvalue singularity. Taking the time delay as the bifurcation parameter, the presence of steady-state bifurcation, Bogdanov–Takens bifurcation, triple zero, and Hopf-zero singularities is demonstrated. In the case when the system has a simple zero eigenvalue, center manifold reduction and normal form theory are used to investigate the stability and the types of steady-state bifurcation. The stability of the zero solution of the system near the simple zero eigenvalue singularity is completely solved.
Glancing angle sputter deposited nanostructures on rotating substrates: Experiments and simulations
Authors: Patzig C. , Karabacak T. , Fuhrmann B. , Rauschenbach B.
Published: November 2008

Ordered arrays of Si nanorods and nanospirals have been produced by ion beam sputter glancing angle deposition of Si on rotating substrates. The substrates were prepatterned with honeycomb and hexagonal-closed-packed arranged Au dots obtained by nanosphere lithography. The effects of template type, substrate rotational speed, height of the artificial Au seeds, and deposition angle θ of the incident flux on the growth of the Si nanostructures is examined. Especially for the deposition of Si on honeycomb templates at different deposition angles, it is shown that the structure of the growing film changes drastically. A continuous film with honeycomblike arranged hillocks on top is deposited at normal incidence. With increased θ, the structure shifts to almost dense films with a mesh of hexagonally arranged pores (θ=70°). Finally, separated rodlike structures with triangular cross section are obtained under glancing angle conditions (θ=85°). In addition, the structural evolution of the glancing angle deposited Si films is compared with oblique angle deposition three-dimensional Monte Carlo simulations. Furthermore, the effects of surface diffusion on the growth of spiral Si nanostructures on nontemplated substrates in experiment and simulation are compared and discussed.
Self-doping and partial oxidation of metal-on-organic interfaces for organic semiconductor devices studied by chemical analysis techniques
Authors: Scholz Sebastian , Huang Qiang , Thomschke Michael , Olthof Selina , Sebastian Philipp , Walzer Karsten , Leo Karl , Oswald Steffen , Corten Cathrin , Kuckling Dirk
Published: November 2008

The performance of organic electronic devices, such as organic light emitting diodes, transistors, or organic solar cells, depends critically on the chemical composition of the metal/organic and organic/metal interfaces which inject or extract charges into or from the device. By combining a number of techniques, such as x-ray photoemission spectroscopy (XPS) sputter depth profiling, XPS itself, secondary ion mass spectrometry, and laser desorption/ionization time-of-flight mass spectrometry, we investigate the reasons for differences in charge injection from metallic bottom and top contacts into either preferentially hole or preferentially electron transporting materials. We find that the deposition of metal onto organic semiconductors creates an organic-inorganic mixed interlayer in between the organic bulk material and the metal. In the case of electron injection, this interlayer acts as highly doped injection layer, while for hole injection, no significant improvement is visible. In addition to the self-doping, some cathode materials form partially oxidized metal-on-organic interfaces caused by oxygen in the residual gas. Depending on the evaporation conditions, the oxygen content varies. The effect of the oxygen incorporation, the origin, and the binding behavior in between the metal-on-organic interlayer is investigated and discussed. In contrast, organic materials evaporated on top of metals create an abrupt interface, where no self-doping effect is observed.
Structural, dynamic, and electronic properties of liquid tin: An ab initio molecular dynamics study
Authors: Calderín L. , González D. J. , González L. E. , López J. M.
Published: November 2008

We report on a study of several structural, dynamic, and electronic properties of liquid Sn at a thermodynamic state close to the triple point (573K) and another one at a higher temperature (1273K). This study has been performed by ab initio molecular dynamics simulations using 205 atoms and around 20ps of simulation time. The calculated static structures show a good agreement with the available experimental data. The dynamic structure factors fairly agree with their experimental counterparts obtained by inelastic x-ray scattering experiments, which display inelastic side peaks. The calculated dispersion relations exhibit a positive dispersion, although not so marked as suggested by the experiment; moreover, its slope at the long-wavelength limit compares favorably with the experimental sound velocity. Electron densities near selected triplets of atoms are similar to those appearing in the solid phases, but these features have an extremely short lifetime, so they should not be considered as solid remnants in the melt.
Fluids of hard natural and Gaussian ellipsoids: A comparative study by integral equation theories
Authors: Perera Aurélien
Published: November 2008

The hard Gaussian overlap (HGO) model for ellipsoids is compared to the hard ellipsoid of revolution (HER) model, in the isotropic fluid phase and within the framework of the Percus–Yevick (PY) and hypernetted chain (HNC) integral equation theories. The former model is often used in place of the latter in many approximate theories. Since the HGO model slightly overestimates the contact distance when the two ellipsoids are perpendicular to each other, it leads to small differences in the Mayer function of the two models, but nearly none in the integrals of these functions and particularly for the second virial coefficients. However, it leads to notable differences in the pair correlation functions, as obtained by the Percus–Yevick and the hypernetted chain theories, especially at high densities. The prediction of the stability of the isotropic phase with respect to orientational order, at high densities, is notably influenced by these small differences. Both theories predict that, for same aspect ratios, the HGO model overestimates the ordering, when compared to the HER model. This explains why the PY approximation predicts ordering for the HGO model with aspect ratio of 1:3, while it does not for the HER model, in accordance with the very first integral equation results obtained for this system, and at variance with many opposite claims from subsequent publications that used the HGO model in place of the HER model.
Effect of grain refinement on enhancing critical current density and upper critical field in undoped MgB2 ex situ tapes
Authors: Malagoli A. , Braccini V. , Tropeano M. , Vignolo M. , Bernini C. , Fanciulli C. , Romano G. , Putti M. , Ferdeghini C. , Mossang E. , Polyanskii A. , Larbalestier D. C.
Published: November 2008

Ex situ powder-in-tube MgB2 tapes prepared with ball-milled, undoped powders showed a strong enhancement of the irreversibility field H∗, the upper critical field Hc2, and the critical current density Jc(H) together with the suppression of the anisotropy of all of these quantities. Jc reached 104 A/cm2 at 4.2 K and 10 T, with an irreversibility field of about 14 T at 4.2 K, and Hc2 of 9 T at 25 K, high values for not-doped MgB2. The enhanced Jc and H∗ values are associated with significant grain refinement produced by milling of the MgB2 powder, which enhances grain boundary pinning, even if at the same time also reducing the connectivity from about 12% to 8%. Although enhanced pinning and diminished connectivity are in opposition, the overall influence of ball milling on Jc is positive because the increased density of grains with a size comparable with the mean free path produces strong electron scattering that substantially increases Hc2, especially Hc2 perpendicular to the Mg and B planes.
Thickness dependence of photoluminescence for tensely strained silicon layer on insulator
Authors: Munguía J. , Bluet J-M. , Baira M. , Marty O. , Bremond G. , Hartmann J. M. , Mermoux M.
Published: November 2008

Strain and crystalline quality of tensely strained silicon on insulator with thickness ranging from 8 to 100 nm have been evaluated by low temperature photoluminescence (PL). The strain conservation in the strained Si layers was checked by Raman spectroscopy. The PL clearly shows the emission related to the strained silicon optical band gap even for strained layers as much as seven times thicker than critical thickness (hc∼15 nm). For very thin layers (9 nm), a 21 meV blueshift is observed in the PL spectra, which corresponds to a 17 meV calculated one coming from quantum confinement in the sSi layer.
Symmetrical frequency response in a split ring resonator based transmission line
Authors: Borja A. L. , Carbonell J. , Boria V. E. , Lippens D.
Published: November 2008

A coplanar waveguide line based on a split ring resonator technology and loaded with metallic strips and capacitances is proposed. The addition of series capacitances to previous unit cell implementations dramatically improves the upper band rejection levels and provides a transmission response almost symmetric. The configuration also exhibits a band pass response with a right-handed character as a result of the balance between advance and delay phase offsets contrary to the conventional left-handed lines. The interpretation is based on an equivalent circuit model, full-wave electromagnetic analysis, and measured responses of a prototype designed for microwave operation.
Defect annihilation and morphological improvement of hydrothermally grown ZnO nanorods by Ga doping
Authors: Escobedo-Morales A. , Pal U.
Published: November 2008

One dimensional zinc oxide nanostructures were grown by a low temperature hydrothermal process. Effects of Ga doping on the growth, crystallization, and defect distribution in them were studied by x-ray diffraction, scanning electron microscopy, photoluminescence, and Fourier-transform infrared spectroscopy techniques. It has been shown that Ga doping improves the morphological homogeneity and optical properties of ZnO nanostructures. Improved morphology of the doped nanostructures have been associated with the catalytic effect of Ga. Effects of Ga doping on the quenching of defect emission and improvement of excitonic emission in ZnO nanostructures are discussed.
Enhanced thermoelectric figure of merit in nanostructured n-type silicon germanium bulk alloy
Authors: Wang X. W. , Lee H. , Lan Y. C. , Zhu G. H. , Joshi G. , Wang D. Z. , Yang J. , Muto A. J. , Tang M. Y. , Klatsky J. , Song S. , Dresselhaus M. S. , Chen G. , Ren Z. F.
Published: November 2008

The dimensionless thermoelectric figure of merit (ZT) of the n-type silicon germanium (SiGe) bulk alloy at high temperature has remained at about one for a few decades. Here we report that by using a nanostructure approach, a peak ZT of about 1.3 at 900 °C in an n-type nanostructured SiGe bulk alloy has been achieved. The enhancement of ZT comes mainly from a significant reduction in the thermal conductivity caused by the enhanced phonon scattering off the increased density of nanograin boundaries. The enhanced ZT will make such materials attractive in many applications such as solar, thermal, and waste heat conversion into electricity.
Origin of the open-circuit voltage in multilayer heterojunction organic solar cells
Authors: Potscavage W. J. , Yoo S. , Kippelen B.
Published: November 2008

From temperature dependent studies of pentacene/C60 solar cells in the dark, the reverse saturation current is found to be thermally activated with a barrier height that corresponds to the difference in energy between the highest occupied molecular orbital of the donor and the lowest unoccupied molecular orbital of the acceptor corrected for vacuum level misalignments and the presence of charge-transfer states. From the reverse saturation current in the dark and the short-circuit current under illumination, the open-circuit voltage can be predicted. Examination of several donor materials supports the relationship between reverse saturation current, this barrier height, and open-circuit voltage.
Investigation of drift in electro-optic polymer waveguides
Authors: Thapliya Roshan , Nakamura Shigetoshi , Kikuchi Takashi
Published: November 2008

The mechanism of the phase drift in electro-optic polymer waveguide devices is presented based on buildup of free ion charge at the electrode-clad interfaces. The difference of the electrode-clad interfaces at the top and bottom electrodes is shown to be important in reducing the drift and that doping of the core with macrocyclic polyethers can suppress this phenomenon. Arrhenius curves of long-term phase drifts using Mach–Zehnder modulators show the activation energies for symmetric electrode interfaces, asymmetric electrode interfaces, and macrocyclic polyether doped cores to be 0.30, 0.28, and 0.15 eV, respectively.
Direct characterization of focusing light by negative refraction in a photonic crystal flat lens
Authors: Tian Jie , Yan Min , Qiu Min , Ribbing Carl G. , Liu Ya-Zhao , Zhang Dao-Zhong , Li Zhi-Yuan
Published: November 2008

We report experimental measurements of the field distribution of the light spot focused by a two-dimensional photonic crystal flat lens at wavelengths 1.51–1.58 μm. The photonic crystal slab is fabricated on a silicon-on-insulator substrate by focused-ion-beam direct milling. We confirm the light focusing by the photonic crystal slab through direct observation of the light spot entering into free space at the end facet of the slab lens. The beam profiles as the function of lateral position are measured and the minimal full width half maximum of the beam at 1.2 μm (0.77λ) is obtained.
Effective surface passivation methodologies for high performance germanium metal oxide semiconductor field effect transistors
Authors: Na H. J. , Lee J. C. , Heh D. , Sivasubramani P. , Kirsch P. D. , Oh J. W. , Majhi P. , Rivillon S. , Chabal Y. J. , Lee B. H. , Choi R.
Published: November 2008

We demonstrate methodologies to improve the interface characteristics between a germanium (Ge) substrate and high-k gate dielectrics. GeON and SiOx were investigated as passivating layers on a Ge surface. Smaller hysteresis and interface state density (Dit) were obtained using SiOx interface layer and p-type metal oxide semiconductor field effect transistors (MOSFETs) fabricated with a gate stack of Ge/SiOx/HfSiO/WN showed about two times higher effective mobility compared to universal Si/SiO2 MOSFET. Because the formation of GeOx at the interface resulted in higher hysteresis and equivalent oxide thickness, the effective suppression of growth of unstable GeOx by SiOx interface layer contributed to the good device characteristics of the fabricated devices.
Quantum-dot light-emitting diodes utilizing CdSe∕ZnS nanocrystals embedded in TiO2 thin film
Authors: Kang Seung-Hee , Kumar Ch. Kiran , Lee Zonghoon , Kim Kyung-Hyun , Huh Chul , Kim Eui-Tae
Published: November 2008

Quantum-dot (QD) light-emitting diodes (LEDs) are demonstrated on Si wafers by embedding core-shell CdSe∕ZnS nanocrystals in TiO2 thin films via plasma-enhanced metallorganic chemical vapor deposition. The n-TiO2∕QDs∕p-Si LED devices show typical p-n diode current-voltage and efficient electroluminescence characteristics, which are critically affected by the removal of QD surface ligands. The TiO2∕QDs∕Si system we presented can offer promising Si-based optoelectronic and electronic device applications utilizing numerous nanocrystals synthesized by colloidal solution chemistry.
Effect of oxide structure on the Fermi-level pinning at metal/Gd2O3 interfaces
Authors: Lipp E. , Eizenberg M. , Czernohorsky M. , Osten H. J.
Published: November 2008

The extent of Fermi-level pinning at metal/Gd2O3 interfaces is studied as a function of oxide structure by comparing the flatband voltage of Ta- and Pt-gated capacitors. The flatband voltage shift between the two metals, which equals the difference in effective work functions, was found to be largest when the oxide is single crystalline (1.30±0.05 V), while lower values are measured when the oxide is domain structured (1.05±0.05V) or amorphous (0.80±0.05V). These results indicate that long-range ordering has a dominant effect on Fermi-level pinning at metal/high-k interfaces.
Evolution in surface morphology of epitaxial graphene layers on SiC induced by controlled structural strain
Authors: Ferralis Nicola , Kawasaki Jason , Maboudian Roya , Carraro Carlo
Published: November 2008

The evolution in the surface morphology of epitaxial graphene films and 6H-SiC(0001) substrates is studied by electron channeling contrast imaging. Whereas film thickness is determined by growth temperature only, increasing growth times at constant temperature affects both internal stress and film morphology. Annealing times in excess of 8–10 min lead to an increase in the mean square roughness of SiC step edges to which graphene films are pinned, resulting in compressively stressed films at room temperature. Shorter annealing times produce minimal changes in the morphology of the terrace edges and result in nearly stress-free films upon cooling to room temperature.
ZnO-based low voltage inverter with low-k/high-k double polymer dielectric layer
Authors: Lee Kimoon , Kim Ki-tae , Lee Kwang H. , Lee Gyubaek , Oh Min Suk , Choi Jeong-M. , Im Seongil , Jang Sungjin , Kim Eugene
Published: November 2008

We report on the fabrication of ZnO-based depletion-load-type inverter composed of two n-channel ZnO thin-film transistors (TFTs) with a low-k poly-4-vinylphenol and high-k poly(vinylidene fluoride-trifluoroethylene) double polymer dielectric. One of the two ZnO channels in the inverter was illuminated by 352 nm wavelength ultraviolet so that the illuminated ZnO channel might be depleted. That ZnO-TFT plays as a driver transistor in the inverter set where the original TFT is used as a load one. The both TFTs show the same mobility of ∼0.3 cm2/V s and our inverter operates with a voltage gain of ∼4 at low supplied voltages (5–7 V), demonstrating a dynamic response of ∼20 ms.
Crystal structure effect on the ferromagnetic correlations in ZnO with magnetic impurities
Authors: Gu Bo , Bulut Nejat , Maekawa Sadamichi
Published: November 2008

We study the ferromagnetism in the compound (Zn,Mn)O within the Haldane–Anderson impurity model by using the quantum Monte Carlo technique and the tight-binding approximation for determining the host band structure and the impurity-host hybridization. This computational approach allows us to determine how the host crystal structure influences the impurity bound state, which plays an important role in the development of the ferromagnetic (FM) correlations between the impurities. We find that the FM correlations are strongly influenced by the crystal structure. In particular, in p-type (Zn,Mn)O, we observe the development of FM correlations with an extended range at low temperatures for wurtzite and zinc-blende crystal structures. However, for the rocksalt structure, no FM correlations are observed between the impurities. In addition, in n-type ZnO with magnetic impurities, the impurity bound state and FM correlations are not found.
Electrical bistable memory device based on a poly(styrene-b-4-vinylpyridine) nanostructured diblock copolymer thin film
Authors: Huang Ching-Mao , Liu Yung-Sheng , Chen Chen-Chia , Wei Kung-Hwa , Sheu Jeng-Tzong
Published: November 2008

This paper describes the performance of a nonvolatile memory device based on a solution-processed poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) diblock copolymer thin film. The Al/PS-b-P4VP/indium tin oxide memory device featuring metal-coordinated 30 nm P4VP cores exhibited an ON/OFF ratio of 2×105, an erase voltage of 0.75 V, a write voltage of −0.5 V, and a retention time of 104 s. The device exhibited a metallic behavior in the ON state, suggesting the formation of metallic filaments through the migration of Al atoms into the P4VP domain during writing. Such nanostructured diblock copolymer thin films open up avenues for fabricating organic memory devices using simple procedures.
Thickness inhomogenities in the organometallic chemical vapor deposition of GaP
Authors: Liu X. , Aspnes D. E.
Published: November 2008

We analyze exponential lateral-thickness variations observed in the growth of GaP on (001) GaAs, thermally generated SiO2, (001) Si, and nanoscopically roughened Si surfaces by organometallic chemical vapor deposition, using as a reference the polycrystalline GaP deposited on the Mo susceptor surrounding the 2in. wafers. We find these variations to be due to differences in the chemical reactivities of the various surfaces toward the generation of a precursor, probably a H–P=Ga–CH3 dimer adduct, by heterogeneous catalysis followed by desorption and diffusion through the gas phase.
Improved wall plug efficiency of a 1.9THz quantum cascade laser by an automated design approach
Authors: Freeman Joshua R. , Marshall Owen , Beere Harvey E. , Ritchie David A.
Published: November 2008

We demonstrate an improvement in the wall plug efficiency in a bound-to-continuum quantum cascade laser operating below 2THz. This was achieved by targeting one perceived weakness in a previous design, extraction from the lower laser state. This targeted improvement was made possible by employing an automated search algorithm to select a design giving rise to specified electronic states. The resulting laser design represents the highest wall plug efficiency below 2THz and the lowest frequency devices to operate in the high-power single plasmon waveguide. The device displays a wall plug efficiency of 1.2% per facet, double the reference design.
Band alignment at metal/organic and metal/oxide/organic interfaces
Authors: Helander M. G. , Wang Z. B. , Qiu J. , Lu Z. H.
Published: November 2008

Charge injection at metal/organic interfaces dictates the performance, lifetime, and stability of organic electronic devices. We demonstrate that interface dipole theory, originally developed to describe Schottky contacts at metal/semiconductor interfaces, can also accurately describe the injection barriers in real organic electronic devices. It is found that theoretically predicted hole injection barriers for various archetype metal/organic and metal/oxide/organic structures are in excellent agreement with values extracted from experimental transport measurements. Injection barriers at metal/organic and metal/oxide/organic interfaces can therefore be accurately predicted based on the knowledge of only a few fundamental material properties of the oxide and organic layers.
Wide and Diffuse Perceptual Modes Characterize Dyslexics in Vision and Audition
Authors: Geiger Gadi , Cattaneo Carmen , Galli Raffaella , Pozzoli Uberto , Lorusso Maria Luisa , Facoetti Andrea , Molteni Massimo
Published: November 2008

We examined the performance of dyslexic and typically reading children on two analogous recognition tasks: one visual and the other auditory. Both tasks required recognition of centrally and peripherally presented stimuli. Dyslexics recognized letters visually farther in the periphery and more diffuse near the center than typical readers did. Both groups performed comparably in recognizing centrally spoken stimuli presented without peripheral interference, but in the presence of a surrounding speech mask (the ‘cocktail-party effect’) dyslexics recognized the central stimuli significantly less well than typical readers. However, dyslexics had a higher ratio of the number of words recognized from the surrounding speech mask, relative to the ones from the center, than typical readers did. We suggest that the evidence of wide visual and auditory perceptual modes in dyslexics indicates wider multi-dimensional neural tuning of sensory processing interacting with wider spatial attention.
Mosquito RUNX4 in the immune regulation of PPO gene expression and its effect on avian malaria parasite infection
Authors: Zou Zhen , Shin Sang Woon , Alvarez Kanwal S. , Bian Guowu , Kokoza Vladimir , Raikhel Alexander S.
Published: November 2008

Prophenoloxidases (PPOs) are key enzymes of the melanization reaction, which is a prominent defense mechanism of arthropods. The mosquito
Aedes aegypti
has ten PPO genes in the genome, four of which (PPO1, PPO3, PPO5, and PPO8) were expressed in response to microbial infection. Cactus depletion resulted in transcriptional activation of these four genes, suggesting this up-regulation to be under the control of the Toll pathway. The silencing of Cactus also led to developmental arrest and death of the avian malaria parasite,
Plasmodium gallinaceum
. We discovered that RUNT-related transcription factor 4 (RUNX4), the orthologue of
Drosophila
Lozenge, bound to the RUNT binding motif in the promoter of mosquito PPO genes and stimulated the expression of
Drosophila
PPO-A1 and PPO3 in S2 cell line. The immune effects caused by Cactus depletion were eliminated by double knockdown of Cactus/RUNX4. These findings suggest that RUNX4 regulates PPO gene expression under the control of the Toll pathway and plays a critical role in restricting parasite development.
Water conservation in irrigation can increase water use
Authors: Ward Frank A. , Pulido-Velazquez Manuel
Published: November 2008

Climate change, water supply limits, and continued population growth have intensified the search for measures to conserve water in irrigated agriculture, the world's largest water user. Policy measures that encourage adoption of water-conserving irrigation technologies are widely believed to make more water available for cities and the environment. However, little integrated analysis has been conducted to test this hypothesis. This article presents results of an integrated basin-scale analysis linking biophysical, hydrologic, agronomic, economic, policy, and institutional dimensions of the Upper Rio Grande Basin of North America. It analyzes a series of water conservation policies for their effect on water used in irrigation and on water conserved. In contrast to widely-held beliefs, our results show that water conservation subsidies are unlikely to reduce water use under conditions that occur in many river basins. Adoption of more efficient irrigation technologies reduces valuable return flows and limits aquifer recharge. Policies aimed at reducing water applications can actually increase water depletions. Achieving real water savings requires designing institutional, technical, and accounting measures that accurately track and economically reward reduced water depletions. Conservation programs that target reduced water diversions or applications provide no guarantee of saving water.
Micrometeorites from the Transantarctic Mountains
Authors: Rochette P. , Folco L. , Suavet C. , van Ginneken M. , Gattacceca J. , Perchiazzi N. , Braucher R. , Harvey R. P.
Published: November 2008

We report the discovery of large accumulations of micrometeorites on the Myr-old, glacially eroded granitic summits of several isolated nunataks in the Victoria Land Transantarctic Mountains. The number (>3,500) of large (>400 μm and up to 2 mm in size) melted and unmelted particles is orders of magnitudes greater than other Antarctic collections. Flux estimates, bedrock exposure ages and the presence of ≈0.8-Myr-old microtektites suggest that extraterrestrial dust collection occurred over the last 1 Myr, taking up to 500 kyr to accumulate based on 2 investigated find sites. The size distribution and frequency by type of cosmic spherules in the >200-μm size fraction collected at Frontier Mountain (investigated in detail in this report) are similar to those of the most representative known micrometeorite populations (e.g., South Pole Water Well). This and the identification of unusual types in terms of composition (i.e., chondritic micrometeorites and spherulitic aggregates similar to the ≈480-kyr-old ones recently found in Antarctic ice cores) and size suggest that the Transantarctic Mountain micrometeorites constitute a unique and essentially unbiased collection that greatly extends the micrometeorite inventory and provides material for studies on micrometeorite fluxes over the recent (≈1 Myr) geological past.
RanGAP1 is a continuous marker of the
Arabidopsis
cell division plane
Authors: Xu Xianfeng Morgan , Zhao Qiao , Rodrigo-Peiris Thushani , Brkljacic Jelena , He Chao Sylvia , Müller Sabine , Meier Iris
Published: November 2008

In higher plants, the plane of cell division is faithfully predicted by the preprophase band (PPB). The PPB, a cortical ring of microtubules and F-actin, disassembles upon nuclear-envelope breakdown. During cytokinesis, the expanding cell plate fuses with the plasma membrane at the cortical division site, the site of the former PPB. The nature of the “molecular memory” that is left behind by the PPB and is proposed to guide the cell plate to the cortical division site is unknown. RanGAP is the GTPase activating protein of the small GTPase Ran, which provides spatial information for nucleocytoplasmic transport and various mitotic processes in animals. Here, we show that, in dividing root cells,
Arabidopsis
RanGAP1 concentrates at the PPB and remains associated with the cortical division site during mitosis and cytokinesis, requiring its N-terminal targeting domain. In a
fass
/
ton2
mutant, which affects PPB formation, RanGAP1 recruitment to the PPB site is lost, while its PPB retention is microtubule-independent. RanGAP1 persistence at the cortical division site, but not its initial accumulation at the PPB requires the 2 cytokinesis-regulating kinesins POK1 and POK2. Depletion of RanGAP by inducible RNAi leads to oblique cell walls and cell-wall stubs in root cell files, consistent with cytokinesis defects. We propose that
Arabidopsis
RanGAP, a continuous positive protein marker of the plant division plane, has a role in spatial signaling during plant cell division.
GDP-mannose pyrophosphorylase is a genetic determinant of ammonium sensitivity in
Arabidopsis thaliana
Authors: Qin Cheng , Qian Weiqiang , Wang Wenfeng , Wu Yue , Yu Chunmei , Jiang Xinhang , Wang Daowen , Wu Ping
Published: November 2008

Higher plant species differ widely in their growth responses to ammonium (NH
4
+
). However, the molecular genetic mechanisms underlying NH
4
+
sensitivity in plants remain unknown. Here, we report that mutations in the
Arabidopsis
gene encoding GDP-mannose pyrophosphorylase (GMPase) essential for synthesizing GDP-mannose confer hypersensitivity to NH
4
+
. The in planta activities of WT and mutant GMPases all were inhibited by NH
4
+
, but the magnitude of the inhibition was significantly larger in the mutant. Despite the involvement of GDP-mannose in both
l
-ascorbic acid (AsA) and N-glycoprotein biosynthesis, defective protein glycosylation in the roots, rather than decreased AsA content, was linked to the hypersensitivity of GMPase mutants to NH
4
+
. We conclude that NH
4
+
inhibits GMPase activity and that the level of GMPase activity regulates
Arabidopsis
sensitivity to NH
4
+
. Further analysis showed that defective N-glycosylation of proteins, unfolded protein response, and cell death in the roots are likely important downstream molecular events involved in the growth inhibition of
Arabidopsis
by NH
4
+
.
Exploring knotting mechanisms in protein folding
Authors: Mallam Anna L. , Morris Elizabeth R. , Jackson Sophie E.
Published: November 2008

One of the most striking topological features to be found in a protein is that of a distinct knot formed by the path of the polypeptide backbone. Such knotted structures represent some of the smallest “self-tying” knots observed in Nature. Proteins containing a knot deep within their structure add an extra complication to the already challenging protein-folding problem; it is not obvious how, during the process of folding, a substantial length of polypeptide chain manages to spontaneously thread itself through a loop. Here, we probe the folding mechanism of YibK, a homodimeric α/β-knot protein containing a deep trefoil knot at its carboxy terminus. By analyzing the effect of mutations made in the knotted region of the protein we show that the native structure in this area remains undeveloped until very late in the folding reaction. Single-site destabilizing mutations made in the knot structure significantly affect only the folding kinetics of a late-forming intermediate and the slow dimerization step. Furthermore, we find evidence to suggest that the heterogeneity observed in the denatured state is not caused by isomerization of the single
cis
proline bond as previously thought, but instead could be a result of the knotting mechanism. These results allow us to propose a folding model for YibK where the threading of the polypeptide chain and the formation of native structure in the knotted region of the protein occur independently as successive events.
Genome-wide analyses of Geraniaceae plastid DNA reveal unprecedented patterns of increased nucleotide substitutions
Authors: Guisinger Mary M. , Kuehl Jennifer V. , Boore Jeffrey L. , Jansen Robert K.
Published: November 2008

Angiosperm plastid genomes are generally conserved in gene content and order with rates of nucleotide substitutions for protein-coding genes lower than for nuclear protein-coding genes. A few groups have experienced genomic change, and extreme changes in gene content and order are found within the flowering plant family Geraniaceae. The complete plastid genome sequence of
Pelargonium
X
hortorum
(Geraniaceae) reveals the largest and most rearranged plastid genome identified to date. Highly elevated rates of sequence evolution in Geraniaceae mitochondrial genomes have been reported, but rates in Geraniaceae plastid genomes have not been characterized. Analysis of nucleotide substitution rates for 72 plastid genes for 47 angiosperm taxa, including nine Geraniaceae, show that values of
dN
are highly accelerated in ribosomal protein and RNA polymerase genes throughout the family. Furthermore,
dN/dS
is significantly elevated in the same two classes of plastid genes as well as in ATPase genes. A relatively high
dN/dS
ratio could be interpreted as evidence of two phenomena, namely positive or relaxed selection, neither of which is consistent with our current understanding of plastid genome evolution in photosynthetic plants. These analyses are the first to use protein-coding sequences from complete plastid genomes to characterize rates and patterns of sequence evolution for a broad sampling of photosynthetic angiosperms, and they reveal unprecedented accumulation of nucleotide substitutions in Geraniaceae. To explain these remarkable substitution patterns in the highly rearranged Geraniaceae plastid genomes, we propose a model of aberrant DNA repair coupled with altered gene expression.
Nanoparticle-induced surface reconstruction of phospholipid membranes
Authors: Wang Bo , Zhang Liangfang , Bae Sung Chul , Granick Steve
Published: November 2008

The nonspecific adsorption of charged nanoparticles onto single-component phospholipid bilayers bearing phosphocholine headgroups is shown, from fluorescence and calorimetry experiments, to cause surface reconstruction at the points where nanoparticles adsorb. Nanoparticles of negative charge induce local gelation in otherwise fluid bilayers; nanoparticles of positive charge induce otherwise gelled membranes to fluidize locally. Through this mechanism, the phase state deviates from the nominal phase transition temperature by tens of degrees. This work generalizes the notions of environmentally induced surface reconstruction, prominent in metals and semiconductors. Bearing in mind that chemical composition in these single-component lipid bilayers is the same everywhere, this offers a mechanism to generate patchy functional properties in phospholipid membranes.
Vibrationally inelastic H + D
2
collisions are forward-scattered
Authors: Goldberg Noah T. , Zhang Jianyang , Koszinowski Konrad , Bouakline Foudhil , Althorpe Stuart C. , Zare Richard N.
Published: November 2008

We have measured differential cross sections (DCSs) for the vibrationally inelastic scattering process H +
o
-D
2
(
v
= 0,
j
= 0,2) → H +
o
-D
2
(
v′
= 1–4,
j′
even). Several different collision energies and nearly the entire range of populated product quantum states are studied. The products are dominantly forward-scattered in all cases. This behavior is the opposite of what is predicted by the conventional textbook mechanism, in which collisions at small impact parameters compress the bond and cause the products to recoil in the backward direction. Recent quasiclassical trajectory (QCT) calculations examining only the
o
-D
2
(
v′
= 3,
j′
) products suggest that vibrationally inelastic scattering is the result of a frustrated reaction in which the D—D bond is stretched, but not broken, during the collision. These QCT calculations provide a qualitative explanation for the observed forward-scattering, but they do not agree with experiments at the lowest values of
j′
. The present work shows that quantum mechanical calculations agree closely with experiments and expands upon previous results to show that forward-scattering is universally observed in vibrationally inelastic H + D
2
collisions over a broad range of conditions.
AIRE regulates T-cell-independent B-cell responses through BAFF
Authors: Lindh Emma , Lind Sara M. , Lindmark Evelina , Hässler Signe , Perheentupa Jaakko , Peltonen Leena , Winqvist Ola , Karlsson Mikael C. I.
Published: November 2008

Autoimmune polyendocrine syndrome type I (APS I) results in multiple endocrine organ destruction and is caused by mutations in the autoimmune regulator gene (AIRE). APS I is characterized by circulating tissue-specific autoantibodies, and the presence of these antibodies is often predictive of organ destruction. The importance of AIRE in ensuring central tolerance by regulating the negative selection of autoreactive T cells has been shown clearly. However, inAire−/−mice the phenotype (i.e., autoantibodies, liver infiltrates of B cells, splenomegaly, and marginal zone B-cell lymphoma) is predominantly B-cell mediated, suggesting an exaggerated activation of B cells. We have studied T-cell-independent B-cell responses in the absence ofAIREand found thatAire−/−mice have an increased response against T-cell-independent type II antigens. We linked this exaggerated response to the elevated serum levels of the B-cell-activating factor of the TNF family (BAFF) that were found both in APS I patients and inAire−/−mice. Transfer ofAire−/−bone marrow into irradiated nude mice resulted in increased percentage of BAFF-expressing antigen-presenting cells compared with wt bone marrow, suggesting a T-cell-independent mechanism behind our findings. Furthermore,invitro experiments showed that AIRE-deficient murine bone marrow-derived dendritic cells produced significantly more BAFF than wt cells when stimulated with IFN-γ but not when stimulated with IL-10. Our results suggest a cell-intrinsic role for AIRE in peripheral dendritic cells by regulating IFN-γ-receptor signaling and point toward complementary mechanisms by which AIRE is involved in maintaining tolerance.
Structural basis of sequence-specific collagen recognition by SPARC
Authors: Hohenester Erhard , Sasaki Takako , Giudici Camilla , Farndale Richard W. , Bächinger Hans Peter
Published: November 2008

Protein interactions with the collagen triple helix play a critical role in collagen fibril formation, cell adhesion, and signaling. However, structural insight into sequence-specific collagen recognition is limited to an integrin-peptide complex. A GVMGFO motif in fibrillar collagens (O denotes 4-hydroxyproline) binds 3 unrelated proteins: von Willebrand factor (VWF), discoidin domain receptor 2 (DDR2), and the extracellular matrix protein SPARC/osteonectin/BM-40. We report the crystal structure at 3.2 Å resolution of human SPARC bound to a triple-helical 33-residue peptide harboring the promiscuous GVMGFO motif. SPARC recognizes the GVMGFO motifs of the middle and trailing collagen chains, burying a total of 720 Å
2
of solvent-accessible collagen surface. SPARC binding does not distort the canonical triple helix of the collagen peptide. In contrast, a critical loop in SPARC is substantially remodelled upon collagen binding, creating a deep pocket that accommodates the phenylalanine residue of the trailing collagen chain (“Phe pocket”). This highly restrictive specificity pocket is shared with the collagen-binding integrin I-domains but differs strikingly from the shallow collagen-binding grooves of the platelet receptor glycoprotein VI and microbial adhesins. We speculate that binding of the GVMGFO motif to VWF and DDR2 also results in structural changes and the formation of a Phe pocket.
Cardiac myosin-binding protein C decorates F-actin: Implications for cardiac function
Authors: Whitten Andrew E. , Jeffries Cy M. , Harris Samantha P. , Trewhella Jill
Published: November 2008

Cardiac myosin-binding protein C (cMyBP-C) is an accessory protein of striated muscle sarcomeres that is vital for maintaining regular heart function. Its 4 N-terminal regulatory domains, C0-C1-m-C2 (C0C2), influence actin and myosin interactions, the basic contractile proteins of muscle. Using neutron contrast variation data, we have determined that C0C2 forms a repeating assembly with filamentous actin, where the C0 and C1 domains of C0C2 attach near the DNase I-binding loop and subdomain 1 of adjacent actin monomers. Direct interactions between the N terminus of cMyBP-C and actin thereby provide a mechanism to modulate the contractile cycle by affecting the regulatory state of the thin filament and its ability to interact with myosin.