bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of quenching on electronic-resonance-enhanced coherent anti-Stokes Raman scattering of nitric oxide
Authors: Roy Sukesh , Kulatilaka Waruna D. , Naik Sameer V. , Laurendeau Normand M. , Lucht Robert P. , Gord James R.
Published: September 2006

We investigate the effects of gas-mixture composition on the electronic-resonance-enhanced coherent anti-Stokes Raman scattering (ERE-CARS) signals of nitric oxide (NO). From previous laser-induced fluorescence (LIF) studies, quenching rates are known to change drastically, by factors of 400–800, in mixtures of CO2∕O2∕N2. The observed ERE-CARS signal remains constant to within 30% whereas LIF signals from NO are predicted to decrease by more than two orders of magnitudes in the same environments. This is very significant for using NO ERE-CARS in high-pressure combustion environments where the electronic quenching rate can vary rapidly as a function of both space and time.
Magnetoelectric effects of nanoparticulate Pb(Zr0.52Ti0.48)O3–NiFe2O4 composite films
Authors: Ryu Hyejin , Murugavel P. , Lee J. H. , Chae S. C. , Noh T. W. , Oh Yoon Seok , Kim Hyung Jin , Kim Kee Hoon , Jang Jae Hyuck , Kim Miyoung , Bae C. , Park J.-G.
Published: September 2006

The authors fabricated Pb(Zr0.52Ti0.48)O3–NiFe2O4 composite films consisting of randomly dispersed NiFe2O4 nanoparticles in the Pb(Zr0.52Ti0.48)O3 matrix. The structural analysis revealed that the crystal axes of the NiFe2O4 nanoparticles are aligned with those of the ferroelectric matrix. The composite has good ferroelectric and magnetic properties. The authors measured the transverse and longitudinal components of the magnetoelectric voltage coefficient, which supports the postulate that the magnetoelectric effect comes from direct stress coupling between magnetostrictive NiFe2O4 and piezoelectric Pb(Zr0.52Ti0.48)O3 grains.
Transportation of molecules with a scanning tunneling microscope
Authors: Zhang Hanjie , Huang Han , He Pimo , Bao Shining , Zhou Wuzong , Richardson Neville V.
Published: September 2006

Transportation of mass molecules from one metal surface to another has been achieved with scanning tunneling microscope tip at room temperature. With scanning monolayer of tetracene on Ag(110) surface, the molecules were removed gradually, leaving ordered stripes on the Ag surface; the ordered stripes are unidirectional nanoscopic molecular rows with a width of about 1.4nm. Scanning the clean Ru(101¯0) sample with the tip, previously adsorbed the tetracene molecules, caused an appearance of the molecules on the Ru surface. Short molecular strips with different widths from 4to20nm were drawn on the Ru surface by a molecule-loaded W tip.
Self-organization of step bunching instability on vicinal substrate
Authors: Pascale A. , Berbezier I. , Ronda A. , Videcoq A. , Pimpinelli A.
Published: September 2006

The authors investigate quantitatively the self-organization of step bunching instability during epitaxy of Si on vicinal Si(001). They show that growth instability evolution can be fitted by power laws L∼tα and A∼tβ (where L is the correlation length and A is the instability amplitude) with critical exponents α∼0.3 and β∼0.5 in good agreement with previous studies and well reproduced by kinetic Monte Carlo simulation. They demonstrate that the main phenomenon controlling step bunching is the anisotropy of surface diffusion. The microscopic origin of the instability is attributed to an easier adatom detachment from SA step, which can be interpreted as a pseudoinverse Ehrlich-Schwoebel barrier [J. Appl. Phys. 37, 3682 (1967); J. Chem. Phys. 44, 1039 (1966)].
Hole-transporting interlayers for improving the device lifetime in the polymer light-emitting diodes
Authors: Lee Tae-Woo , Kim Mu-Gyeom , Kim Sang Yeol , Park Sang Hun , Kwon Ohyun , Noh Taeyong , Oh Tae-Sik
Published: September 2006

The authors report the effect of thermal treatment of hole-transporting interlayers between a polymeric hole injection layer and an emitting layer (EML) on the luminous efficiency and the lifetime performance in blue polymer light-emitting diodes. As the thermal annealing temperature of the interlayer increased, the hole mobility of the interlayer tended to decrease, which results in reducing the hole current injected into the EML in the devices. Hence, the device luminous efficiency decreased due to lower electron-hole balance. Nevertheless, the device lifetime increased, which can be attributed to the formation of the thicker interlayer and the better defined interlayer/EML interface.
Hydrogen and oxygen on InP nanowire surfaces
Authors: Schmidt T. M.
Published: September 2006

Recently great progress have been obtained with nanowires for electrical and optical applications. Due to the large surface-to-volume ratio of these nanostructures, of particular interest is the understanding of the unknown and hard to determine experimentally surface structure and the electronic effects due to surface states. In this letter the author investigate the structural and electronic properties of hydrogen passivation and the oxidation of surface InP nanowires by ab initio density functional theory. Our calculations show that hydrogen passivation is a chemisorbed process that removes the surface states, opening up the band gap. Our results for oxygen adsorbed on the hydrogen passivated InP nanowires show that there are many configurations where the oxygens are chemisorbed processes. The oxygens introduce energy levels back inside the band gap that can work as nonradiative recombination centers and can explain some experiments, such as the low luminescence observed in InP nanostructures.
Polymer supported carbon nanotube arrays for field emission and sensor devices
Authors: Watts Paul C. P. , Lyth Stephen M. , Mendoza Ernest , Silva S. Ravi P.
Published: September 2006

The authors report a simple method for providing a polymer support structure for carbon nanotube (CNT) arrays for device applications. This method has a twofold effect: firstly it secures the nanotubes to the substrate and secondly it significantly decreases the threshold field for field emission from 26.2to9.7V∕μm. This method ensures that the main body and tips of the CNTs are polymer-free and therefore can also be applied to CNT sensor array device fabrication.
Metal-insulator-semiconductor-type organic light-emitting transistor on plastic substrate
Authors: Nakamura Kenji , Hata Takuya , Yoshizawa Atsushi , Obata Katsunari , Endo Hiroyuki , Kudo Kazuhiro
Published: September 2006

The authors report the characteristics of novel metal-insulator-semiconductor-type organic light-emitting transistors (MIS-OLETs). The drain current and luminescent intensity of the MIS-OLET can be controlled by changing hole injection carriers by applying a gate bias voltage. In addition, the high performance (400cd∕m2 at VD=−8V) of MIS-OLETs fabricated on a plastic substrate as well as on a glass substrate is demonstrated and described.
Plastron properties of a superhydrophobic surface
Authors: Shirtcliffe Neil J. , McHale Glen , Newton Michael I. , Perry Carole C. , Pyatt F. Brian
Published: September 2006

Most insects and spiders drown when submerged during flooding or tidal inundation, but some are able to survive and others can remain submerged indefinitely without harm. Many achieve this by natural adaptations to their surface morphology to trap films of air, creating plastrons which fix the water-vapor interface and provide an incompressible oxygen-carbon dioxide exchange surface. Here the authors demonstrate how the surface of an extremely water-repellent foam mimics this mechanism of underwater respiration and allows direct extraction of oxygen from aerated water. The biomimetic principle demonstrated can be applied to a wide variety of man-made superhydrophobic materials.
Crystallization of Si3N4 layers and its influences on the microstructure and mechanical properties of ZrN∕Si3N4 nanomultilayers
Authors: Dong Yunshan , Zhao Wenji , Yue Jianling , Li Geyang
Published: September 2006

Zr N ∕ Si 3 N 4 nanomultilayers with different layer thicknesses of Si3N4 were synthesized to study the crystallization of Si3N4 and its effects on the microstructure and mechanical properties of multilayers. Results indicated that influenced by the template effects of crystalline ZrN layers, amorphous Si3N4 layers were crystallized into a rocksaltlike pseudocrystal structure when their thickness was less than 0.9nm. Then crystallized Si3N4 layers grew epitaxially with ZrN and formed strong columnar crystals, accompanied with a remarkable increase in hardness. When its thickness exceeds 1.1nm, the subsequently deposited Si3N4 grows as amorphous, blocking the epitaxial growth and leading to a quick decline of hardness.
Electrically adjustable intersubband absorption of a GaN∕AlN superlattice grown on a transistorlike structure
Authors: Baumann Esther , Giorgetta Fabrizio R. , Hofstetter Daniel , Leconte Sylvain , Guillot Fabien , Bellet-Amalric Edith , Monroy Eva
Published: September 2006

The authors report on electromodulated intersubband (ISB) absorption experiments on AlN∕GaN superlattices (SLs) grown on a transistorlike structure. A sample containing five SL periods shows two distinct absorption peaks related to ISB transitions in the SL and in the two dimensional electron gas located at the interface of the lowest SL barrier and the underlying GaN buffer. The ratio of those two absorption peaks can be adjusted by applying an external field, which influences the overall band structure and, more specifically, the free carrier density in the SL. This is a proof of concept of an on-off electro-optical modulator at 1.5μm.
Explosion dynamics of dusty plasma liquids induced by laser ablation on suspended dust particles
Authors: Chu Hong-Yu , Liao Chen-Ting , I Lin
Published: September 2006

Dusty plasma liquids can be formed by suspending negatively charged micrometer sized dust particles in a low pressure glow discharge. We investigate the dynamical behaviors of the expanding plume generated by the ablation on one of the suspended particles using a focused nanosecond pulsed laser, through monitoring the white light emission intensity and dust particle trajectories. In the initial 10μs, the diameter of the expanding plume scales as D∝P−0.37t0.31, where P is the background pressure. The surrounding dust particles start to be driven away radially after tens of microseconds. The diameter of the expanding cavity (plasma bubble) with dust depletion scales as D∝t0.33.
Pseudoheterodyne detection for background-free near-field spectroscopy
Authors: Ocelic Nenad , Huber Andreas , Hillenbrand Rainer
Published: September 2006

The authors present a detection technique for scattering-type near-field optical microscopy capable of background interference elimination in the entire near-UV to far-IR spectral range. It simultaneously measures near-field optical signal amplitude and phase by interferometric detection of scattered light utilizing a phase-modulated reference wave. They compare its background suppression efficiency to other known methods and experimentally show that it provides a reliable near-field optical material contrast even in the case where both noninterferometric and homodyne interferometric detection methods fail.
Grazing-incidence x-ray diffraction study of pentacene thin films with the bulk phase structure
Authors: Yoshida Hiroyuki , Sato Naoki
Published: September 2006

The structure of pentacene thin films in the bulk phase having interplane spacing of d(001)=1.44nm grown on SiO2 was investigated using grazing-incidence x-ray diffraction. The films were prepared with two different methods: one treated with an organic solvent after vacuum deposition and the other thermally treated. Both films are similar in structure to the single crystal reported by Campbell et al. [Acta Crystallogr. 15, 289 (1962)].
Luminescence efficiency at 1.5μm of Er-doped thick SiO layers and Er-doped SiO∕SiO2 multilayers
Authors: Wora Adeola G. , Jambois O. , Miska P. , Rinnert H. , Vergnat M.
Published: September 2006

The luminescence from Er-doped thin films is studied in two different systems. The first one is a SiO single layer. The second one is a SiO∕SiO2 multilayer allowing us to obtain size-controlled silicon nanocrystals. In both systems, the annealing-temperature dependence of the luminescence is investigated. It is shown that the optimal annealing temperatures are equal to 700 and 1050°C for the single layer and the multilayer, respectively. Moreover the luminescence efficiency at 1.5μm is one order of magnitude higher in the single Er-doped SiO layer. These results are discussed in relation to the formation of silicon nanoparticles with annealing treatments.
In situ deformation apparatus for time-of-flight neutron diffraction:Texture development of polycrystalline ice Ih
Authors: McDaniel S. , Bennett K. , Durham W. B. , Waddington E. D.
Published: September 2006

This article documents a new in situ deformation apparatus built for neutron diffraction investigations of polycrystalline materials in low-temperature environments and the first experiment in which it was used. We performed texture analysis of fine-grained polycrystalline D2O ice Ih deformed uniaxially between 230 and 240K using time-of-flight neutron diffraction on the high-pressure preferred orientation diffractometer at the Manuel Lujan, Jr. Neutron Scattering Center at Los Alamos National Laboratory. The new deformation apparatus operates at 1atm of ambient pressure and over temperatures in the range of 77K<T<298K, and accommodates up to 667N of uniaxially applied load. It is suitable for diffraction studies of any bulk polycrystalline material, ideally cylindrical in shape, and is adaptable to multiple neutron spectrometers, including those at other polychromatic and monochromatic neutron facilities. The first experiment on a hexagonal ice sample demonstrates development of fiber texture in the direction of the applied load. The equipment has many applications to earth science, glaciology, and ice engineering.
Electric field dependent dielectric properties and high tunability of BaZrxTi1−xO3 relaxor ferroelectrics
Authors: Maiti Tanmoy , Guo R. , Bhalla A. S.
Published: September 2006

This letter reports the E-field tunable behavior of the environmental friendly lead-free perovskite BaZrxTi1−xO3 (x=0.50 and 0.60) relaxor ceramics in the temperature range from 300to30K. dc electric field dependence of dielectric behavior of the ceramics has been studied. The results have been analyzed in relation to tunability (%) and K factor of the tunable dielectric materials. It is shown that manipulating the Zr:Ti concentration in BaZrxTi1−xO3 ceramics and optimizing the applied dc bias field the properties for specific applications in tunable filters, phase shifters, antennas, etc., can be tailored in the temperature range from 100to300K.
Role of low temperature rapid thermal annealing in post-laser-annealed p-channel metal-oxide-semiconductor field effect transistor
Authors: Ong K. K. , Pey K. L. , Lee P. S. , Wee A. T. S. , Wang X. C. , Tung C. H. , Tang L. J. , Chong Y. F.
Published: September 2006

In this letter, the authors study the importance of a low temperature anneal in the removal of crystalline defects resulting from pulsed laser annealing of preamorphized ultrashallow p+∕n junction. Using an additional low thermal budget rapid thermal annealing at 600°C for 60s, suppression of junction leakage current of two orders in a single-pulse laser annealing and one order in a ten-pulse laser annealing is achieved through a reduction of the residual crystalline defects that could not be annihilated by laser annealing. p-channel metal-oxide-semiconductor field effect transistors with good electrical characteristics can be obtained using pulsed laser annealing followed by a low thermal budget rapid thermal annealing.
Rankine-Hugoniot relations of an axial shock in cylindrical non-neutral plasma
Authors: He Yong , Hu Xiwei , Hu Yemin , Jiang Zhonghe , Lü Jianhong
Published: September 2006

The Rankine-Hugoniot relations of an axial shock in cylindrical non-neutral plasma with current, electric and magnetic field are presented. These relations are all dependent on the radius of cylindrical plasma, and markedly different from the one-dimensional (i.e., nonradially dependent) case. These two-dimensional Rankine-Hugoniot relations cause at least two important new results. First, the radial profiles of the shock downstream parameters are always different from the upstream profiles due to the magnetic effects. Second, the critical Mach number for the shock existence will depend on the shock carried current (i.e., magnetic field). As an example, a set of shock downstream profiles is provided numerically when the upstream profiles are taken as a kind of typical equilibrium profiles of a Z-pinch-Bennett profiles. By comparing the downstream profiles to the corresponding upstream profiles, the dependents of both the amplitudes and profiles of the downstream parameters on the shock carried current are shown.
Balanced homodyne detection of second-harmonic generation from isolated subwavelength emitters
Authors: Le Xuan L. , Brasselet S. , Treussart F. , Roch J.-F. , Marquier F. , Chauvat D. , Perruchas S. , Tard C. , Gacoin T.
Published: September 2006

The authors demonstrate the association of two-photon nonlinear microscopy with balanced homodyne detection for investigating second-harmonic radiation properties at nanoscale dimensions. Variation of the relative phase between second-harmonic and fundamental beams is retrieved, as a function of the absolute orientation of the nonlinear emitters. Sensitivity down to a few photons per second in the spatiotemporal mode of the local oscillator is obtained. This value is high enough to efficiently detect the coherent second-harmonic emission from a single KTiOPO4 crystal of subwavelength size.
X-ray absorption fine structure measurement with a 9V electric battery x-ray emitter
Authors: Mitsuya Shota , Ishii Hideshi , Kawai Jun , Tanaka Keiichi
Published: September 2006

X-ray absorption spectral analysis is a well known technique for analyzing the chemical environment of an element in a specimen. It has been believed that high intensity and monochromatized x rays such as the synchrotron radiation are required for an x-ray absorption experiment. In the present study, however, we demonstrate that the x-ray absorption spectral measurement of transition metal foils with an energy resolution of 10eV is possible with a combination of a 9V dry electric battery pyroelectric x-ray generator and a superconducting microcalorimeter.
Application of regioregular polythiophene in spintronic devices: Effect of interface
Authors: Majumdar Sayani , Laiho R. , Laukkanen P. , Väyrynen I. J. , Majumdar Himadri S. , Österbacka R.
Published: September 2006

The authors report on fabrication and characterization of a polymeric spin valve with the conjugated polymer regioregular (poly 3-hexylthiophene) (RRP3HT) as the spacer layer. The device structure is La0.67Sr0.33MnO3 (LSMO)/polymer/Co, with half-metallic, spin-polarized LSMO acting as the spin-injecting electrode. The spin valve shows behavior similar to a magnetic tunnel junction though the nonmagnetic spacer layer (∼100nm) is much thicker than the tunneling limit. They attribute this behavior to the formation of a thin spin-selective tunneling interface between LSMO and RRP3HT caused by RRP3HT, chemically attaching to LSMO as observed by x-ray photoelectron spectroscopy measurement. This gives rise to ∼80% magnetoresistance (MR) at 5K and ∼1.5% MR at room temperature. They found that by introducing monolayer of different organic insulators between LSMO and RRP3HT the spin-selective interface is destroyed and the spin injection is reduced. Their results show that organic materials are promising candidates for spintronic applications.
Band-to-band character of photoluminescence from InN and In-rich InGaN revealed by hydrostatic pressure studies
Authors: Franssen G. , Suski T. , Perlin P. , Teisseyre H. , Khachapuridze A. , Dmowski L. H. , Plesiewicz J. A. , Kamińska A. , Kurouchi M. , Nanishi Y. , Lu H. , Schaff W.
Published: September 2006

The authors studied the hydrostatic pressure dependence of photoluminescence (PL) from In-rich InxGa1−xN with In contents x between 0.58 and 1.00. The observed PL pressure coefficients of 20–25meV∕GPa agree well with previously reported experimental and theoretical values of the band gap pressure coefficient, from which they conclude that band-to-band recombination is responsible for PL emission. This contrasts with earlier reports, where relatively low PL pressure coefficients were interpreted as evidence of the involvement of strongly localized states in the PL emission. The reported observation of band-to-band recombination in In-rich InGaN is encouraging from the point of view of the construction of light emitters, since band-to-band recombination is more efficient than recombination via localized states. Furthermore, significant bowing of the band gap pressure coefficient in In-rich InxGa1−xN, as predicted by theory, is confirmed.
Halftoning band gap of InAs∕InP quantum dots using inductivelycoupled argon plasma-enhanced intermixing
Authors: Nie D. , Mei T. , Xu C. D. , Dong J. R.
Published: September 2006

Inductively coupled argon plasma-enhanced intermixing of InAs∕InP quantum dots grown on InP substrate is investigated. Intermixing is promoted by the near-surface defects generated by plasma exposure in annealing at a temperature of 600°C for 30s. The annealing results in a maximum differential band-gap blueshift of 106nm but a thermal shift of only 10nm. Band-gap halftones are obtained by controlling the amount of near-surface defects via wet chemical etching on the plasma-exposed InP cap layer. No degradation of quantum-dot crystal quality due to the process has been observed as evidenced by photoluminescence intensity.
Dark spot formation mechanism in organic light emitting diodes
Authors: Kim Soo Young , Kim Kwang Young , Tak Yoon-Heung , Lee Jong-Lam
Published: September 2006

The authors report electroluminescence degradation in organic light emitting diode operated at a high current density of 500mA∕cm2 under nitrogen ambient. The turn-on voltage increased from 6to10V, and a number of dark spots were produced when the device was operated for 420min. Microscope image showed that dark spots are related to many protrusions and hollows formed on Al electrode. X-ray diffraction and scanning photoemission microscope spectra indicate that the Joule heat from high electric field induced the crystallization of 4′-bis[N-(1-naphtyl)-N-phenyl-amino]biphenyl, forming dark spots via peeling off of the Al cathode.
Highly controlled orientation of CaBi4Ti4O15 using a strong magnetic field
Authors: Suzuki Tohru S. , Kimura Masahiko , Shiratsuyu Kosuke , Ando Akira , Sakka Yoshio , Sakabe Yukio
Published: September 2006

The texture of feeble magnetic ceramics can be controlled by a strong magnetic field. When the magnetic susceptibility of the c axis is smaller than that of the other axes, the c axis aligns perpendicular to the magnetic field; however, the direction is randomly oriented on the plane perpendicular to the magnetic field. The authors demonstrate in this letter that a highly controlled texture in bismuth titanate, which has a c-axis susceptibility smaller than the other axes, can be achieved using a two-step magnetic field procedure. This highly controlled orientation is effective for improving the electromechanical coupling coefficient.
Diffraction of Light from Sources of Finite Dimensions
Authors: Godfrey GH
Published: September 2006

The distribution of light intensity in the diffraction pattern of continuous light sources is
treated analytically for Fraunhofer diffraction phenomena. Sources and
diffracting apertures of any dimensions are first discussed, and a result of
general application is derived which relates the illumination and dimensions of
the diffraction pattern to the dimensions of the source and aperture. A source
consisting of a luminous strip is considered in more detail, the form of the
pattern is derived for such a source, and tables are supplied to facilitate
numerical evaluation. Consideration is given to the maxima and minima of
intensity in the image, and the conditions under which these are observable are
indicated. In particular, attention is drawn to certain diffraction effects
which do not seem to have been previously recorded and which are in agreement
with the theory. These effects consist of faint but visually discernible
fringes associated with the image of a strip when viewed
through a narrow slit. Applications to the optics of the telescope and
spectroscope are discussed.
Observations on the Variable Source of Cosmic Radio Frequency Radiation in the Constellation of Cygnus
Authors: Bolton JG , Stanley GJ
Published: September 2006

An account is given of investigations on a strong variable source of radio frequency energy in the constellation of Cygnus, including a determination of the size and celestial coordinates of the
source and a study of the variations over a frequency range from 60 to 200 Mc/s. The frequency spectra are compared with those of galactic and solar radiation.
The position of the source is found to be in a region of relatively low stellar density and not coinciding with an outstanding stellar object. A discussion of limits of distance and possible nature of the source is given.
Cyclic Voltammetric and E.P.R. Spectroscopic Studies on Apical Substituent Effects in Radical Anions of 9-Substituted and 9,10-Disubstituted Nitroethanoanthracenes
Authors: Lay PA , Norris RK , Witting PK
Published: September 2006

Cyclic voltammetry and electron paramagnetic resonance spectroscopy were used to examine apical substituent effects on the properties of Me2SO solutions of the radical anions from 9-substituted and 9,10-disubstituted 2- and 3-nitro-9,10-dihydro-9,10-ethanoanthracenes (1)-(24). The reductions of the nitro group are, in general, reversible at 100 mV s-1 and at 20°, except where there are coupled intra-or inter-molecular electron or proton transfer reactions with aliphatic bridgehead substituents, such as a carboxylic acid or iodine. The substituent effects for the meta- and para-nitroethanoanthracene systems are both similar and additive. This similarity in the meta and para polar substituent effects is attributed to the orthogonality of the π*(ArNO2/ArNO2-) orbital with the σ* orbital of the carbon substituent (C-X) groups at the bridgehead positions. Overall, the meta substituent effect was slightly lower than that for corresponding simple meta-nitrobenzyl systems, but the para-nitro systems showed substituent effects that are a factor of 2 smaller than that for corresponding simple para-nitrobenzyl systems. These linear correlations between the substituent effects and redox potentials have been used to estimate the redox potentials of irreversible systems, which are required for digital simulations of reactions involving nitroaryl radical anions. Only small substituent effects are present in hyperfine coupling with the aliphatic and aromatic protons of the nitroaromatic radical anions of ethanoanthracenes (1)-(13), but a clear trend to lower nitrogen hyperfine values was observed with increasing electron-withdrawing ability of the apical substituent. In addition, no spin density was transferred to the benzylic bridgehead substituent in any of the nitro radical anions studied, clearly demonstrating that the bond between the bridgehead substituent and the carbon at a benzylic position is orthogonal to the π-system of the nitroaromatic ring bearing the odd electron.
The surface oxidation potential of human neuromelanin reveals a spherical architecture with a pheomelanin core and a eumelanin surface
Authors: Bush William D. , Garguilo Jacob , Zucca Fabio A. , Albertini Alberto , Zecca Luigi , Edwards Glenn S. , Nemanich Robert J. , Simon John D.
Published: September 2006

Neuromelanin (NM) isolated from the substantia nigra region of the human brain was studied by scanning probe and photoelectron emission microscopies. Atomic force microscopy reveals that NM granules are comprised of spherical structures with a diameter of ≈30 nm, similar to that observed forSepiacuttlefish, bovine eye, and human eye and hair melanosomes. Photoelectron microscopy images were collected at specific wavelengths of UV light between 248 and 413 nm, using the spontaneous-emission output from the Duke OK-4 free electron laser. Analysis of the data establishes a threshold photoionization potential for NM of 4.5 ± 0.2 eV, which corresponds to an oxidation potential of −0.1 ± 0.2 V vs. the normal hydrogen electrode (NHE). The oxidation potential of NM is within experimental error of the oxidation potential measured for human eumelanosomes (−0.2 ± 0.2 V vs. NHE), despite the presence of a significant fraction of the red pigment, pheomelanin, which is characterized by a higher oxidation potential (+0.5 ± 0.2 V vs. NHE). Published kinetic studies on the early chemical steps of melanogenesis show that in the case of pigments containing a mixture of pheomelanin and eumelanin, of which NM is an example, pheomelanin formation occurs first with eumelanin formation predominantly occurring only after cysteine levels are depleted. Such a kinetic model would predict a structural motif with pheomelanin at the core and eumelanin at the surface, which is consistent with the measured surface oxidation potential of the ≈30-nm constituents of NM granules.
Increased sensitivity after repeated stimulation of residual spatial channels in blindsight
Authors: Sahraie Arash , Trevethan Ceri T. , MacLeod Mary Joan , Murray Alison D. , Olson John A. , Weiskrantz Lawrence
Published: September 2006

Lesions of the occipital cortex result in areas of cortical blindness affecting the corresponding regions of the patient's visual field. The traditional view is that, aside from some spontaneous recovery in the first few months after the damage, when acute effects have subsided the areas of blindness are absolute and permanent. It has been found, however, that within such field defects some residual visual capacities may persist in the absence of acknowledged awareness by the subject (blindsight type 1) or impaired awareness (type 2). Neuronal pathways mediating blindsight have a specific and narrow spatial and temporal bandwidth. A group of cortically blind patients (
n
= 12) carried out a daily detection “training” task over a 3-month period, discriminating grating visual stimuli optimally configured for blindsight from homogeneous luminance-matched stimuli. No feedback was given during the training. Assessment of training was by psychophysical measurements carried out before and after training and included detection of a range of spatial frequencies (0.5–7 cycles per degree), contrast detection at 1 cycle per degree, clinical perimetry, and subjective estimates of visual field defect. The results show that repeated stimulation by appropriate visual stimuli can result in improvements in visual sensitivities in the very depths of the field defect.
Microvascular Display of Xanthine Oxidase and NADPH Oxidase in the Spontaneously Hypertensive Rat
Authors: DELANO FRANK A. , PARKS DALE A. , RUEDI JULIE M. , BABIOR BERNARD M. , SCHMID‐SCHÖNBEIN GEERT W.
Published: September 2006

Objective: Oxygen free radical production in hypertension may be associated with elevated arteriolar tone and organ injury. Previous results suggest an enhanced level of oxygen free radical formation in microvascular endothelium and in circulating neutrophils associated with xanthine oxidase activity in the spontaneously hypertensive rats (SHR) compared with their normotensive controls, the Wistar Kyoto rats (WKY). The aim of this study was to gain more detailed understanding of where oxidative enzymes are located in the microcirculation.

Methods: An approach was developed to delineate the cellular distribution of two selected oxidative enzymes, xanthine oxidase and nicotinamide adenine dinucleotide phosphate (NADPH) dependent oxidase (protein 67‐kDa fraction). Immunolabeling with peroxidase substrate was utilized, which permits full delineation of the primary antibody in all microvascular structures of the mesentery.

Results: Xanthine oxidase is present in the endothelium of all segments of the microcirculation, in mast cells, and in parenchymal cells of the mesentery. NADPH oxidase can be detected in the endothelium, leukocytes, and mast cells and with lower levels in parenchymal cells. The mesentery of WKY and SHR has similar enzyme distributions with enhancements on the arteriolar and venular side of the microcirculation that coincide with the sites of enhanced free radical production recently reported. Immune label measurements under standardized conditions indicate that both enzymes are significantly enhanced in the SHR. Adrenalectomy, which serves to reduce the blood pressure and free radical production of the SHR to normotensive levels, leads to a reduction of NADPH and xanthine oxidase to normotensive levels, while supplementation of adrenalectomized SHR with dexamethasone significantly increases the oxidase expression in several parts of the microcirculation to levels above the WKY rats.

Conclusion: The results indicate that enhanced expression of NADPH and xanthine oxidase in the SHR depends on an adrenal pathway that is detectable in the arteriolar and venular network at high and low pressure regions of the circulation.
Inhibition of NAD(P)H Oxidase Alleviates Impaired NOS‐dependent Responses of Pial Arterioles in Type 1 Diabetes Mellitus
Authors: MAYHAN WILLIAM G. , ARRICK DENISE M. , SHARPE GLENDA M. , PATEL KAUSHIK P. , SUN HONG
Published: September 2006

Objective: The goal was to identify the role of NAD(P)H oxidase in cerebrovascular dysfunction in type 1 diabetes mellitus (T1D).

Methods: In a first series of studies, rats were assigned to nondiabetic, diabetic (streptozotocin; 50 mg/kg IP), nondiabetic‐apocynin (40 mg/kg/day in drinking water)‐treated and diabetic‐apocynin‐treated groups. Two to three months later, the authors examined in vivo responses of pial arterioles to nitric oxide synthase (NOS)‐dependent (acetylcholine and adenosine diphosphate (ADP)) and ‐independent (nitroglycerin) agonists. Next, they used Western blot analysis to examine protein levels for subunits of NAD(P)H oxidase in cerebral microvessels and parietal cortex tissue of nondiabetic and diabetic rats. Finally, they measured superoxide production by parietal cortex tissue in nondiabetic and diabetic rats.

Results: Acetylcholine‐ and ADP‐induced dilatation of pial arterioles was impaired in diabetic compared to nondiabetic rats. In addition, while apocynin did not alter responses in nondiabetic rats, apocynin alleviated T1D‐induced impairment of NOS‐dependent vasodilatation. In addition, p47phox and gp91phox proteins were elevated in cerebral microvessels and parietal cortex tissue, respectively, of diabetic compared to nondiabetic rats. Further, basal production of superoxide was increased in diabetic compared to nondiabetic rats and apocynin decreased this basal production.

Conclusions: The findings suggest that T1D impairs NOS‐dependent reactivity of cerebral arterioles by a mechanism related to the formation of superoxide via activation of NAD(P)H oxidase.
Acupuncture Reduces Experimental Renovascular Hypertension Through Mechanisms Involving Nitric Oxide Synthases
Authors: KIM DAVID D. , PICA ARNALDO M. , DURÁN RICARDO G. , DURÁN WALTER N.
Published: September 2006

Objective:To test the hypothesis that acupuncture on stomach 36 point (ST‐36) reduces hypertension by activating nitric oxide synthase signaling mechanisms.

Methods:The authors used the two‐kidney, one‐clip renal hypertension (2K1C) hamster model with electroacupuncture treatment.

Results:Thirty‐minute daily electroacupuncture treatment for 5 days reduced mean arterial pressure from 160.0 ± 7.6 to 128.0 ± 4.3 mmHg (mean ± SEM), compared to 115.0 ± 7.2 mmHg in sham‐operated hamsters. Electroacupuncture increased periarteriolar NO concentration from 309.0 ± 21.7 nM to 417.9 ± 20.9 nM in the 2K1C hamster cheek pouch microcirculation when measured with NO‐sensitive microelectrodes. Hypertension reduced endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) proteins relative to the sham‐operated control, as measured by Western blotting. Electroacupuncture prevented the reduction of eNOS and nNOS associated with hypertension and showed even higher eNOS and nNOS expressions than sham‐operated control in stomach and cheek pouch tissues, which are on the stomach meridian. Analysis of liver tissue, a non‐stomach‐meridian organ, indicated that electroacupuncture did not have a significant benefit in terms of enhanced expressions of eNOS and nNOS in the treated 2K1C hypertensive group.

Conclusions:Activation of eNOS and nNOS is one of the mechanisms through which ST‐36 electroacupuncture reduces blood pressure; this reduction works through the stomach meridian.
The Formin mDia Regulates GSK3β through Novel PKCs to Promote Microtubule Stabilization but Not MTOC Reorientation in Migrating Fibroblasts
Authors: Eng Christina H. , Huckaba Thomas M. , Gundersen Gregg G.
Published: September 2006

In migrating cells, external signals polarize the microtubule (MT) cytoskeleton by stimulating the formation of oriented, stabilized MTs and inducing the reorientation of the MT organizing center (MTOC). Glycogen synthase kinase 3β (GSK3β) has been implicated in each of these processes, although whether it regulates both processes in a single system and how its activity is regulated are unclear. We examined these issues in wound-edge, serum-starved NIH 3T3 fibroblasts where MT stabilization and MTOC reorientation are triggered by lysophosphatidic acid (LPA), but are regulated independently by distinct Rho GTPase-signaling pathways. In the absence of other treatments, the GSK3β inhibitors, LiCl or SB216763, induced the formation of stable MTs, but not MTOC reorientation, in starved fibroblasts. Overexpression of GSK3β in starved fibroblasts inhibited LPA-induced stable MTs without inhibiting MTOC reorientation. Analysis of factors involved in stable MT formation (Rho, mDia, and EB1) showed that GSK3β functioned upstream of EB1, but downstream of Rho-mDia. mDia was both necessary and sufficient for inducing stable MTs and for up-regulating GSK3β phosphorylation on Ser9, an inhibitory site. mDia appears to regulate GSK3β through novel class PKCs because PKC inhibitors and dominant negative constructs of novel PKC isoforms prevented phosphorylation of GSK3β Ser9 and stable MT formation. Novel PKCs also interacted with mDia in vivo and in vitro. These results identify a new activity for the formin mDia in regulating GSK3β through novel PKCs and implicate novel PKCs as new factors in the MT stabilization pathway.
Phosphoprotein Enriched in Astrocytes-15 kDa Expression Inhibits Astrocyte Migration by a Protein Kinase Cδ-dependent Mechanism
Authors: Renault-Mihara François , Beuvon Frédéric , Iturrioz Xavier , Canton Brigitte , De Bouard Sophie , Léonard Nadine , Mouhamad Shahul , Sharif Ariane , Ramos Joe W. , Junier Marie-Pierre , Chneiweiss Hervé
Published: September 2006

Phosphoprotein enriched in astrocytes-15 kDa (PEA-15), a phosphoprotein enriched in astrocytes, inhibits both apoptosis and proliferation in normal and cancerous cells. Here, analysis of PEA-15 expression in glioblastoma organotypic cultures revealed low levels of PEA-15 in tumor cells migrating away from the explants, regardless of the expression levels in the originating explants. Because glioblastomas are highly invasive primary brain tumors that can originate from astrocytes, we explored the involvement of PEA-15 in the control of astrocyte migration. PEA-15−/− astrocytes presented an enhanced motility in vitro compared with their wild-type counterparts. Accordingly, NIH-3T3 cells transfected by green fluorescent protein-PEA-15 displayed a reduced migration. Reexpression of PEA-15 restored PEA-15−/− astrocyte motility to wild-type levels. Pharmacological manipulations excluded a participation of extracellular signal-regulated kinase/mitogen-activated protein kinase, phosphatidylinositol 3-kinase/Akt, and calcium/calmodulin-dependent protein kinase II in this effect of PEA-15. In contrast, treatment by bisindolylmaleimide, Gö6976, and rottlerin, and chronic application of phorbol 12-myristate 13-acetate and/or bryostatin-1 indicated that PKCδ mediated PEA-15 inhibition of astrocyte migration. PEA-15−/− astrocytes constitutively expressed a 40-kDa form of PKCδ that was down-regulated upon PEA-15 reexpression. Together, these data reveal a new function for PEA-15 in the inhibitory control of astrocyte motility through a PKCδ-dependent pathway involving the constitutive expression of a catalytic fragment of PKCδ.
Myristoylated, Alanine-rich C-Kinase Substrate Phosphorylation Regulates Growth Cone Adhesion and Pathfinding
Authors: Gatlin Jesse C. , Estrada-Bernal Adriana , Sanford Staci D. , Pfenninger Karl H.
Published: September 2006

Repellents evoke growth cone turning by eliciting asymmetric, localized loss of actin cytoskeleton together with changes in substratum attachment. We have demonstrated that semaphorin-3A (Sema3A)-induced growth cone detachment and collapse require eicosanoid-mediated activation of protein kinase Cε (PKCε) and that the major PKCε target is the myristoylated, alanine-rich C-kinase substrate (MARCKS). Here, we show that PKC activation is necessary for growth cone turning and that MARCKS, while at the membrane, colocalizes with α3-integrin in a peripheral adhesive zone of the growth cone. Phosphorylation of MARCKS causes its translocation from the membrane to the cytosol. Silencing MARCKS expression dramatically reduces growth cone spread, whereas overexpression of wild-type MARCKS inhibits growth cone collapse triggered by PKC activation. Expression of phosphorylation-deficient, mutant MARCKS greatly expands growth cone adhesion, and this is characterized by extensive colocalization of MARCKS and α3-integrin, resistance to eicosanoid-triggered detachment and collapse, and reversal of Sema3A-induced repulsion into attraction. We conclude that MARCKS is involved in regulating growth cone adhesion as follows: its nonphosphorylated form stabilizes integrin-mediated adhesions, and its phosphorylation-triggered release from adhesions causes localized growth cone detachment critical for turning and collapse.
The Structure of Escherichia coli Signal Recognition Particle Revealed by Scanning Transmission Electron Microscopy
Authors: Mainprize Iain L. , Beniac Daniel R. , Falkovskaia Elena , Cleverley Robert M. , Gierasch Lila M. , Ottensmeyer F. Peter , Andrews David W.
Published: September 2006

Structural studies on various domains of the ribonucleoprotein signal recognition particle (SRP) have not converged on a single complete structure of bacterial SRP consistent with the biochemistry of the particle. We obtained a three-dimensional structure for Escherichia coli SRP by cryoscanning transmission electron microscopy and mapped the internal RNA by electron spectroscopic imaging. Crystallographic data were fit into the SRP reconstruction, and although the resulting model differed from previous models, they could be rationalized by movement through an interdomain linker of Ffh, the protein component of SRP. Fluorescence resonance energy transfer experiments determined interdomain distances that were consistent with our model of SRP. Docking our model onto the bacterial ribosome suggests a mechanism for signal recognition involving interdomain movement of Ffh into and out of the nascent chain exit site and suggests how SRP could interact and/or compete with the ribosome-bound chaperone, trigger factor, for a nascent chain during translation.
Enhancement of U4/U6 Small Nuclear Ribonucleoprotein Particle Association in Cajal Bodies Predicted by Mathematical Modeling
Authors: Klingauf Mirko , Stanĕk David , Neugebauer Karla M.
Published: September 2006

Spliceosomal small nuclear ribonucleoprotein particles (snRNPs) undergo specific assembly steps in Cajal bodies (CBs), nonmembrane-bound compartments within cell nuclei. An example is the U4/U6 di-snRNP, assembled from U4 and U6 monomers. These snRNPs can also assemble in the nucleoplasm when cells lack CBs. Here, we address the hypothesis that snRNP concentration in CBs facilitates assembly, by comparing the predicted rates of U4 and U6 snRNP association in nuclei with and without CBs. This was accomplished by a random walk-and-capture simulation applied to a three-dimensional model of the HeLa cell nucleus, derived from measurements of living cells. Results of the simulations indicated that snRNP capture is optimal when nuclei contain three to four CBs. Interestingly, this is the observed number of CBs in most cells. Microinjection experiments showed that U4 snRNA targeting to CBs was U6 snRNP independent and that snRNA concentration in CBs is ∼20-fold higher than in nucleoplasm. Finally, combination of the simulation with calculated association rates predicted that the presence of CBs enhances U4 and U6 snRNP association by up to 11-fold, largely owing to this concentration difference. This provides a chemical foundation for the proposal that these and other cellular compartments promote molecular interactions, by increasing the local concentration of individual components.
C2B Polylysine Motif of Synaptotagmin Facilitates a Ca2+-independent Stage of Synaptic Vesicle Priming In Vivo
Authors: Loewen Carin A. , Lee Soo-Min , Shin Yeon-Kyun , Reist Noreen E.
Published: September 2006

Synaptotagmin I, a synaptic vesicle protein required for efficient synaptic transmission, contains a highly conserved polylysine motif necessary for function. Using Drosophila, we examined in which step of the synaptic vesicle cycle this motif functions. Polylysine motif mutants exhibited an apparent decreased Ca2+affinity of release, and, at low Ca2+, an increased failure rate, increased facilitation, and increased augmentation, indicative of a decreased release probability. Disruption of Ca2+binding, however, cannot account for all of the deficits in the mutants; rather, the decreased release probability is probably due to a disruption in the coupling of synaptotagmin to the release machinery. Mutants exhibited a major slowing of recovery from synaptic depression, which suggests that membrane trafficking before fusion is disrupted. The disrupted process is not endocytosis because the rate of FM 1-43 uptake was unchanged in the mutants, and the polylysine motif mutant synaptotagmin was able to rescue the synaptic vesicle depletion normally found in sytnullmutants. Thus, the polylysine motif functions after endocytosis and before fusion. Finally, mutation of the polylysine motif inhibits the Ca2+-independent ability of synaptotagmin to accelerate SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor)-mediated fusion. Together, our results demonstrate that the polylysine motif is required for efficient Ca2+-independent docking and/or priming of synaptic vesicles in vivo.