bluuebunny/crossref_metadata_2025 huggingface dataset:
Time evolution of electron energy distribution function and plasma parameters in pulsed and unbalanced magnetron argon discharge
Authors: Seo Sang-Hun , In Jung-Hwan , Chang Hong-Young , Han Jeon-Geon
Published: August 2005

The temporal behavior of the electron energy distribution function and plasma parameters in the vicinity of the substrate have been investigated in detail by performing time-resolved probe measurements in a pulsed and unbalanced magnetron argon discharge. A 20-kHz midfrequency unipolar dc pulse with an on-time average power of 160W and a duty cycle of 50% was applied to the metallic cathode target. It was found that the high-energy electrons with energies higher than the sheath potential energy are generated within a few microseconds after the dc pulse is turned on and the electron energy distribution functions during the pulse-on period show a bi-Maxwellian distribution with the high-energy electron group. In the afterglow after the dc pulse is turned off, the initial fast decay of the high-energy electrons and the subsequent diffusive slower decay of the low-energy electrons were observed. This temporal behavior of the electron energy distribution function reflected two-fold decay characteristics of electron density and electron temperature when approximated by a biexponential function with two characteristic decay times and an initial fast decay time of less than a few microseconds and a subsequent slower decay time of few tens of microseconds were observed. The temporal behavior of the other plasma parameters were presented and these results were explained in view of electron heating by deeply penetrating the high-voltage cathode sheath and electron transport.
Energy transfers and locality in magnetohydrodynamic turbulence
Authors: Verma Mahendra K. , Ayyer Arvind , Chandra Amar V.
Published: August 2005

The shell-to-shell energy transfer rates for magnetohydrodynamic (MHD) turbulence are computed analytically, which shows local energy transfer rates from velocity to velocity, velocity to magnetic, magnetic to velocity, and magnetic to magnetic fields for nonhelical MHD in the inertial range. It is also found that for kinetic-energy dominated MHD fluid, there is a preferential shell-to-shell energy transfer from kinetic to magnetic energy; the transfer is reversed for magnetic-energy dominated MHD fluid. This property is probably the reason for the asymptotic value of Alfvén ratio to be close to 0.5. The analytical results are in close agreement with recent numerical results. When magnetic and kinetic helicities are turned on, the helical contributions are opposite to the corresponding nonhelical contributions. The helical energy transfers have significant nonlocal components.
Intersubband absorption of strain-compensated Si1−xGex valence-band quantum wells with 0.7⩽x⩽0.85
Authors: Fromherz T. , Meduňa M. , Bauer G. , Borak A. , Falub C. V. , Tsujino S. , Sigg H. , Grützmacher D.
Published: August 2005

Strain-compensated, p-type SiGe quantum wells with a high Ge concentration of up to 85% have been grown on commercially available Si0.5Ge0.5 pseudosubstrates by molecular-beam epitaxy. Structural investigations by transmission electron microscopy and high-resolution x-ray reflection and diffraction showed that at a growth temperature around T=300°C, samples in excellent compliance with the design parameters, comparatively sharp interfaces, and negligible increase of growth-induced surface roughness can be grown. Comparison of polarization-dependent intersubband absorption measurements with simulated intersubband absorption spectra shows that for the quantum wells investigated in this work, the hole eigenstates, their in-plane dispersion, and the polarization-dependent intersubband transition matrix elements are accurately described by a strain-dependent, six-band k∙p Luttinger-Kohn Hamiltonian in which only one fitting parameter—the intersubband transition linewidth—is used.
Onset of centrifugal convection in a magnetic-fluid-saturated porous medium
Authors: Saravanan S. , Yamaguchi H.
Published: August 2005

This paper concerns the influence of magnetic field on the onset of centrifugal convection in a magnetic-fluid-filled differentially heated porous layer placed in zero-gravity environment by linear stability theory. The axis of rotation of the layer is placed anywhere within its boundaries, which leads to an alternating direction of the centrifugal body force. The critical centrifugal Rayleigh number, the critical wave number, and the eigenfunctions corresponding to two-dimensional flow pattern at the threshold are calculated using a combination of analytical and numerical methods. Results show significant effects even for low magnetic-field strength when the axis location is located near the cold boundary. It is found that the magnetic field has a destabilizing effect and can be suitably adjusted depending on the axis location and particle magnetization to induce more developed convection currents.
Nanomechanical resonance studies of carbon nanotube peapod bundles
Authors: Jaroenapibal P. , Chikkannanavar S. B. , Luzzi D. E. , Evoy S.
Published: August 2005

Filled carbon nanotubes represent a class of tunable nanoscale materials that could provide both high-quality resonance and sensing specificity for nanoresonator-based devices. We have studied the mechanical properties of C60-filled single-walled carbon nanotube bundles through observation of their mechanical resonances in a transmission electron microscope. X-ray diffraction was used to qualitatively study the filling of C60 in the bulk material. Electron diffraction was used to confirm the filling of each bundle prior to the measurement of individual mechanical resonance frequencies. The electron-diffraction pattern revealed a C60 spacing periodicity of 9.97 Å within the lumen of the nanotubes, which is close to the theoretical equilibrium spacing of R0=10.05Å in bulk C60. An average ratio of (Eb∕ρ)1∕2=13230±3187m∕s was observed for the unfilled bundles, compared with a ratio of (Eb∕ρ)1∕2=19002±2307m∕s for C60-filled bundles. Such values indicate an increase of the average bending modulus by as much as 170% in C60-filled bundles. A dependence of this ratio on the diameter of the structures was also observed. This dependence is explained by the increased importance of intertube slipping in bundles of larger diameter.
Effect of the surface-plasmon resonance on the emission properties of rhodamine 6G infiltrated in synthetic opals
Authors: Ishikawa Keiji , Okubo Tatsuya
Published: August 2005

We investigate the spectrally narrowed emission (SNE) from rhodamine 6G infiltrated in synthetic opals enhanced by the surface-plasmon resonance effect of Ag particles anchored on the internal surface of the synthetic opals. At a larger number density of Ag particles, SNE is observed at a lower pump intensity, and the intensity is reduced to one-tenth without Ag. The enhancement factor is qualitatively reproduced by theoretical calculations as a function of the amount of Ag particles. These results indicate that the enhancement is caused by the surface-plasmon resonance.
On using large-eddy simulation for the prediction of noise from cold and heated turbulent jets
Authors: Bodony Daniel J. , Lele Sanjiva K.
Published: August 2005

The results of a series of large-eddy simulations of heated and unheated jets using approximately 106 grid points are presented. The computations were performed on jets at operating conditions originally investigated by Tanna in the late 1970s [H. K. Tanna, “An experimental study of jet noise Part I: Turbulent mixing noise,” J. Sound Vib., 50, 405 (1977)]. Three acoustic Mach numbers are investigated (Uj∕a∞=0.5, 0.9, and 1.5) at cold (constant stagnation temperature) and heated conditions (Tj∕T∞=1.8, 2.7, and 2.3, respectively). The jets’ initial annular shear layers are thick relative to experimental jets and are quasi-laminar with superimposed disturbances from linear instability theory. It is observed that qualitative changes in the jets’ mean- and turbulent field structure with Uj and Tj are consistent with previous experimental data. However, the jets exhibit a faster centerline mean velocity decay rate relative to the existing data, with a corresponding 3–4 % over-prediction of the peak root-mean-square level. The acoustic pressure fluctuations in the far field are analyzed in detail. The accuracy of the overall sound pressure level predictions is found to be a strong function of the jet Mach number, with the lowest speed jets being the least accurate. At all conditions the peak acoustic frequency occurs at approximately St=fDj∕Uj=0.25. The limited resolution of the computations is shown to impact the radiated sound by yielding effectively low-pass filtered versions of the experimental spectra, with a maximum frequency of St≈1.2.
Single-component light-emitting electrochemical cell fabricated from cationic polyfluorene: Effect of film morphology on device performance
Authors: Edman Ludvig , Liu Bin , Vehse Martin , Swensen James , Bazan Guillermo C. , Heeger Alan J.
Published: August 2005

Planar light-emitting electrochemical cells (LECs) were prepared by drop casting the conjugated polyelectrolyte poly(9,9-bis[6′-(N,N,N,-trimethylammonium)hexyl]fluorene-co-alt-1,4-phenylene) bromide (PFN+Br−) onto substrates patterned with micrometer-sized interelectrode (Au) gaps. When operated at room temperature (RT), such LECs exhibit a gap-size-dependent turn-on voltage for light emission, but when operated at 140°C, the turn-on voltage is essentially gap-size independent and close to the band gap of PFN+Br−. This temperature dependence is consistent with operation below and above the melting temperature (Tm=130°C) of PFN+Br− and is consequently a signature of anion mobility. The RT morphology of PFN+Br− is dependent on the film preparation process: slow evaporation of the solvent via drop casting produces a partially crystalline film, while a fast evaporation via spin casting produces a glassy film. The glassy spin-cast film can, however, be transformed into a partially crystalline film by slow cooling (0.5°C∕min) from an elevated temperature (180°C) to RT. The photoluminescence (PL) from a partially crystalline film is slightly blueshifted and its vibronic structure better resolved than the PL from a glassy spin-cast film.
Nuclear-magnetic-resonance measurements of the hydrogen dynamics in nanocrystalline graphite
Authors: Stanik E. , Majer G. , Orimo S. , Ichikawa T. , Fujii H.
Published: August 2005

Hydrogen-loaded nanocrystalline graphite samples have been prepared by mechanical milling under a hydrogen atmosphere. Milling vials and balls made of agate and ZrO2 have been used to prepare samples with hydrogen contents between 1 and 2wt%. The proton nuclear-magnetic-resonance (H1-NMR) spectra of these samples are well represented by the sum of a broad Gaussian and a more narrow Lorentzian line corresponding to hydrogen in C–H covalent bonds as well as to hydrogen in methyl groups. The temperature dependence of the Lorentzian line can be ascribed to a hindered rotation of the methyl groups. The corresponding activation enthalpy of about 0.12eV has been deduced from the spin-lattice relaxation rates between 250 and 450K. Below about 200K the relaxation rates are temperature independent but they depend strongly on the NMR frequency and on the parameters of the sample preparation. The relaxation due to paramagnetic impurities as well as the cross relaxation of the proton spins with spins of quadrupolar impurity nuclei are proposed to contribute significantly to the measured spin-lattice relaxation rates.
Effects of deposition temperature on the mechanical and physical properties of silicon nitride thin films
Authors: Walmsley B. A. , Liu Y. , Hu X. Z. , Bush M. B. , Winchester K. J. , Martyniuk M. , Dell J. M. , Faraone L.
Published: August 2005

This study investigates the mechanical and physical properties of low-temperature plasma-enhanced chemical-vapor-deposited silicon nitride thin films, with particular respect to the effect of deposition temperature. The mechanical properties of the films were evaluated by both nanoindentation and microcantilever beam-bending techniques. The cantilever beam specimens were fabricated from silicon nitride thin films deposited on (100) silicon wafer by bulk micromachining. The density of the films was determined from quartz crystal microbalance measurements, as well as from the resonant modes of the cantilever beams, which were mechanically excited using an atomic force microscope. It was found that both the Young’s modulus and density of the films were significantly reduced with decreasing deposition temperature. The decrease in Young’s modulus is attributed to the decreasing material density. The decrease in density with decreasing deposition temperature is believed to be due to the slower diffusion rates of the deposited species, which retarded the densification of the film during the deposition process.
Mixed two-stream filamentation modes in a collisional plasma
Authors: Bret A. , Deutsch C.
Published: August 2005

The effects of collisions on the most unstable modes encountered in relativistic electron-beam plasma interaction are investigated. These modes are a mix between two-stream and filamentation modes. It is analytically proven that as long as the effective collision frequency ν is much smaller than the plasma frequency ωp, the maximum growth rate is just reduced, and eventually canceled, by ν when collisions are accounted for. An analytic model for the fluid case is developed.
Analytical solution of the time evolution of an entangled electron spin pair in a double quantum dot nanostructure
Authors: Blaauboer M.
Published: August 2005

Using master equations, we present an analytical solution of the time evolution of an entangled electron spin pair which can occupy 36 different quantum states in a double quantum dot nanostructure. This solution is exact, given a few realistic assumptions, and takes into account relaxation and decoherence rates of the electron spins as phenomenological parameters. Our systematic method of solving a large set of coupled differential equations is straightforward and can be used to obtain analytical predictions of the quantum evolution of a large class of complex quantum systems, for which until now commonly numerical solutions have been sought.
Decay of a magnetic-field-aligned Alfvén wave into inertial and kinetic Alfvén waves in plasmas
Authors: Shukla P. K. , Stenflo L.
Published: August 2005

A simple description of three-wave decay interactions involving a magnetic-field-aligned dispersive Alfvén wave (DAW) pump and two dispersive (either inertial or kinetic) Alfvén waves that are propagating obliquely to the external magnetic-field direction in a uniform plasma is presented. The nonlinear dispersion relations and growth rates are obtained. The present results are useful for understanding the origin of constant-amplitude pump-driven nonthermal DAWs in ionospheric, magnetospheric, and heliospheric plasmas.
Contact effects of solution-processed polymer electrodes: Limited conductivity and interfacial doping
Authors: Wang J. Z. , Chang J. F. , Sirringhaus H.
Published: August 2005

Contact effects between solution processed conducting polymer electrodes with semiconducting polymers in field effect transistors are investigated. Limited conductivity of polymer electrodes and interfacial doping of the active semiconducting polymer by the conducting polymer electrode are found to be two important factors in determining the performance of polymer field effect transistors with printed conducting polymer electrodes.
Large magnetoresistance ratio of 10% by Fe50Co50 layers for current-confined-path current-perpendicular-to-plane giant magnetoresistance spin-valve films
Authors: Fukuzawa Hideaki , Yuasa Hiromi , Hashimoto Susumu , Iwasaki Hitoshi , Tanaka Yoichiro
Published: August 2005

We have realized a large magnetoresistance (MR) ratio of 10.2% by current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) spin-valve films having current-confined-path (CCP) structure formed by AlCu-NOL (nano-oxide-layer). CPP-GMR with conventional Co90Fe10 pinned and free layers showed an MR ratio and a ΔRA (the change of resistance area product) were 4% and 20mΩμm2, respectively, at a small RA (resistance area product) of 500mΩμm2. By replacing the Co90Fe10 layers by Fe50Co50 layers both for pinned and free layers, we have successfully realized a MR ratio and a ΔRA of 7.5% and 37.5mΩμm2, respectively, at a small RA of 500mΩμm2. Moreover, a large MR ratio of 10.2% and a large ΔRA of 418mΩμm2 were realized at a relatively large RA of 4100mΩμm2. This large MR ratio by using Fe50Co50 layers was due to a larger spin-dependent interface scattering factor γ of 0.72 for the interface between Fe50Co50 and Cu, which was improved from a γ of 0.62 for the interface between Co90Fe10 and Cu.
Room-temperature ferromagnetism in Cu-doped ZnO thin films
Authors: Buchholz D. B. , Chang R. P. H. , Song J.-Y. , Ketterson J. B.
Published: August 2005

A series of copper-doped zinc oxide films were grown by pulsed-laser ablation. Films grown under conditions that produced n-type ZnO were nonmagnetic while those grown under conditions that produced p-type were ferromagnetic with a Curie temperature above 350 K. The magnetic moment per copper atom decreased as the copper concentration increased. An explanation for this result is proposed based on the distance between nearest-neighbor copper atoms.
Low-loss percolative dielectric composite
Authors: Xu Jianwen , Wong C. P.
Published: August 2005

In this letter, we report a modified percolative polymer composite that has a low dielectric loss (tanδ∼0.02@10KHz, comparable to that of the polymer matrix), a high dielectric constant (k>100@10KHz, about 30 times higher than that of the polymer matrix), and a low frequency dependence. This high-k polymer hybrid is filled with self-passivated micro- and nano-aluminum particles. The self-passivation of an aluminum particle results in dense nanoscale insulating Al2O3 shells outside of the metallic spheres, which allows the electrons in the metallic core to tunnel through it, and thereby the aluminum/polymer composites exhibit a high dielectric constant as a percolation system; on the other hand, the insulating oxide layer restricts the electron transfer between aluminum particles, thus leading to a very low loss of the composites.
Fabrication and performance of blue GaN-based vertical-cavity surface emitting laser employing AlN∕GaN and Ta2O5∕SiO2 distributed Bragg reflector
Authors: Kao Chih-Chiang , Peng Y. C. , Yao H. H. , Tsai J. Y. , Chang Y. H. , Chu J. T. , Huang H. W. , Kao T. T. , Lu T. C. , Kuo H. C. , Wang S. C. , Lin C. F.
Published: August 2005

GaN-based vertical-cavity surface emitting laser with 3 λ cavity and hybrid mirrors, consisting of the 25 pairs AlN∕GaN dielectric Bragg reflector and the 8 pairs Ta2O5∕SiO2, was fabricated. The laser action was achieved under the optical pumping at room temperature with a threshold pumping energy density of about 53mJ∕cm2. The laser emits 448 nm blue wavelength with a linewidth of 0.25 nm and the laser beam has a degree of polarization of about 84%.
Improving charge-injection balance and cathode transmittance of top-emitting organic light-emitting device with p-type silicon anode
Authors: Ma G. L. , Ran G. Z. , Xu A. G. , Xu Y. H. , Qiao Y. P. , Chen W. X. , Dai L. , Qin G. G.
Published: August 2005

Both charge-injection balance and high transmittance for the cathode are important to achieve high electroluminescence (EL) efficiency for a top-emitting organic light-emitting device (TEOLED) fabricated on silicon substrate. In this letter, by optimizing the electrical resistivity of the p-type silicon chip used as the anode and applying a Yb∕Au double layer cathode with high electron-injection property and high transmittance, the TEOLED with a configuration of p-type silicon∕thermal grown SiO2∕NPB∕Alq3∕Yb∕Au exhibits a higher EL efficiency than those of the TEOLEDs each with a Si chip as the anode reported previously. Its current efficiency is almost equal to that of a TEOLED with the same configuration except for an indium tin oxide anode.
Resonant double grating waveguide structures as enhancement platforms for two-photon fluorescence excitation
Authors: Soria S. , N. A. Thayil K. , Badenes G. , Bader M. A. , Selle A. , Marowsky G.
Published: August 2005

We report a strong enhancement of two-photon fluorescence (TPF) excitation in the evanescent field of a double grating waveguide structure (DGWS). For a suitable combination of wavelength, polarization, and angular orientation of the incident laser light DGWSs show resonant behavior resulting in a large field enhancement at the waveguide surface. We demonstrate that at resonance, TPF spectroscopy reveals a 330-fold enhancement of the fluorescence signal of a tetramethylrhodamine thin film prepared from a picomolar aqueous solution. This shows the large potential of DGWSs as TPF-based high-sensitivity sensor platforms for biotechnological and biophysical application.
Nitrogen-induced suppression of an indium-gallium interdiffusion in InxGa1−xAs1−yNy∕GaAs multiple-quantum wells
Authors: Mussler Gregor , Däweritz Lutz , Ploog Klaus H.
Published: August 2005

In this letter, we present x-ray diffraction (XRD) measurements on as-grown and annealed (In,Ga)As∕GaAs and (In,Ga)(As,N)∕GaAs multiple-quantum wells grown on GaAs (001) substrates. Concerning the (In,Ga)As material system, we observe a shift of the envelope in the XRD curves of the annealed samples. This shift can be explained by an indium–gallium interdiffusion across the (In,Ga)As∕GaAs interfaces. A diffusion model is employed to simulate the envelope shift which yields an activation energy of 0.8 eV. Regarding the XRD curves of the (In,Ga)(As,N) samples, no annealing-induced shift of the envelope is observed. Hence, we conclude that the incorporation of nitrogen suppresses the indium–gallium interdiffusion. Several models are discussed to explain this observation.
Long-range third-harmonic generation in air using ultrashort intense laser pulses
Authors: Théberge F. , Luo Q. , Liu W. , Hosseini S. A. , Sharifi M. , Chin S. L.
Published: August 2005

The generation of a powerful third-harmonic pulse in atmospheric air has been controlled over long-distance propagation using divergent and negatively chirped fundamental pulses. The cofilamentation of the high-intensity fundamental and third-harmonic pulses was observed over long propagation distance using the Lidar technique. The high peak intensity and the extremely broad spectral content generated by both fundamental and third-harmonic pulses imply promising applications for atmospheric remote sensing of pollutants and bioaerosols.
Large positive and negative Goos-Hänchen shifts from a weakly absorbing left-handed slab
Authors: Wang Li-Gang , Zhu Shi-Yao
Published: August 2005

We theoretically show that the Goos-Hänchen (GH) shifts [F. Goos and H. Hänchen, Ann. Phys. 1, 333 (1947)] of the TE- and TM-polarized beams reflected from a slab of the weakly absorbing left-handed material can be large positive near the resonant transmission if the absorption of the slab is sufficiently weak. The GH shift of the TM-polarized reflected beam can be large negative or positive near the Brewster angle.
High Pr-content (Tb0.2Pr0.8)(Fe0.4Co0.6)1.93−xBx magnetostrictive alloys
Authors: Liu J. J. , Ren W. J. , Li J. , Zhao X. G. , Liu W. , Zhang Z. D.
Published: August 2005

High Pr-content (Tb0.2Pr0.8)(Fe0.4Co0.6)1.93−xBx magnetostrictive alloys (0.05⩽x⩽0.15) with a single cubic Laves phase were synthesized by arc-melting and subsequent annealing. The Curie temperature, Tc, and the lattice parameter, a, of the Laves phase in the alloys increase with increasing the boron content up to x=0.10, which is ascribed to the preferential occupation of boronin the interstitial sites of the Laves phase. The addition of a small amount of boron to the(Tb0.2Pr0.8)(Fe0.4Co0.6)1.93 alloy reduces the magnetocrystalline anisotropy constant K1 and improves the magnetostriction λa=λ‖−λ⊥ at relatively low magnetic fields at room temperature. The composition dependence of the ratio λa∕K1 for (Tb0.2Pr0.8)(Fe0.4Co0.6)1.93−xBx alloys reaches a maximum value at x=0.10, suggesting that the (Tb0.2Pr0.8)(Fe0.4Co0.6)1.83B0.1 alloy should be a good candidate material for magnetostriction applications.
Spontaneous spin-filter effect across EuS∕GaAs heterojunction
Authors: Trbovic Jelena , Ren Cong , Xiong Peng , von Molnár Stephan
Published: August 2005

We study current transport across a EuS∕GaAs heterojunction (HJ) modulated by the filtering action of the ferromagnetic semiconductor EuS in zero external magnetic field. Analysis of the current-voltage (I-V) characteristics of the current injected from EuS into GaAs across the HJ yields a value for the Zeeman splitting of the EuS conduction band of (0.48±0.12)eV at 5 K. The change in the barrier height at the HJ mimics the change of the spontaneous magnetization of EuS, i.e., it has Brillouin like characteristics with a TC of 17 K. Utilizing the experimentally obtained values for the Zeeman splitting as input parameters, we analyze the I-V characteristics for unpolarized electrons injected from GaAs, to estimate the polarization detection efficiency as a function of bias and temperature below 30 K.
Enhanced photocatalytic activity of ZnO nanotetrapods
Authors: Wan Q. , Wang T. H. , Zhao J. C.
Published: August 2005

The photocatalytic characteristics of the tetrapod-branched ZnO nanostructures synthesized by thermal evaporation method are investigated. The fitting of absorbance maximum plot versus time indicates an exponential decay, suggesting the photodegradation of Rhodamine B catalyzed by the ZnO nanotetrapod is a pseudo first-order reaction. These results demonstrate that the photocatalytic activity of ZnO nanotetrapod is much better than that of P25 TiO2 and ZnO powders. The slow electron/hole recombine rate due to the abundant surface states, as well as the high surface-to-volume ratio will effectively enhance the photocatalytic activity of the ZnO nanotetrapod.
Extruded single-mode high-index-core one-dimensional microstructured optical fiber with high index-contrast for highly nonlinear optical devices
Authors: Feng Xian , Monro Tanya M. , Petropoulos Periklis , Finazzi Vittoria , Richardson David J.
Published: August 2005

We report the fabrication of a high-index-core one-dimensional microstructured optical fiber incorporating with high index-contrast layers, using extrusion technique for preform fabrication. Single mode guidance and a high effective nonlinearity of 260±30W−1km−1 were observed in the fiber at 1.55μm, highlighting the potential of such fibers for use in nonlinear optical devices.
Photoluminescence decay dynamics of transparent silica glass prepared from nanometer-sized silica particles
Authors: Yamada Tomoko , Uchino Takashi
Published: August 2005

The time-resolved photoluminescence (PL) decays are measured for transparent amorphous silica prepared from solid-phase sintering of nanometer-sized silica particles, which has recently been shown to exhibit a unique white PL emission under ultraviolet excitation [T. Uchino and T. Yamada, Appl. Phys. Lett. 85, 1164 (2004)]. Unlike usual PL processes observed in normal silica glass, it is shown that the present PL results from trapping-controlled migration of photoexcited carriers and their radiative recombination.
An improved band-anticrossing model – including the positional dependence of nitrogen – for InGaNAs∕GaAs quantum well lasers
Authors: Qiu Y. N. , Rorison J. M.
Published: August 2005

The positional dependence of the localized nitrogen (N) within the quantum well is included with the band-anti-crossing model that describes the interaction of the GaInAs conduction band with the localized N defect. It is found that N located at the center of the well interacts more strongly with the InGaAs conduction band than N localized near the edge of the quantum well. Different distributions of N are investigated by studying the conduction band edge shift, energy level splitting, dipole moments, and gain. These quantities are found to be highly dependent upon the position of the N.
Solubility and electrical transport properties of thiolated single-walled carbon nanotubes
Authors: Cui J. B. , Daghlian C. P. , Gibson U. J.
Published: August 2005

Single-walled carbon nanotubes have been modified using dodecanethiol as the reaction agent. The thiolated nanotubes form a stable suspension in toluene, and can be used for Langmuir-Blodgett deposition of monolayers. The nanotube conductance decreases by three orders of magnitude and acquires a gate dependence with a memory effect. The conductance for the on and off states with 0V applied to the gate differs by more than two orders of magnitude. These effects are explained in terms of a chemical reaction between the tube wall and the thiol. The thiolation process is also observed on the exposure of the nanotubes to toluene solutions of dodecanethiol-stabilized Au nanoparticles. The nanoparticles can thus be used for labeling or manipulating the location of the chemical reaction sites on the tube wall. The reaction is followed using optical-absorption measurements.
Optical tuning of three-dimensional photonic crystals fabricated by femtosecond direct writing
Authors: McPhail Dennis , Straub Martin , Gu Min
Published: August 2005

In this letter, we report on an optically tunable three-dimensional photonic crystal that exhibits main gaps in the 3–4μm range. The photonic crystal is manufactured via a femtosecond direct writing technique. Optical tuning is achieved by a luminary polling technique with a low-power polarized laser beam. The refractive index variation resulting from liquid-crystal rotation causes a shift in the photonic band gap of up to 65 nm with an extinction of transmission of up to 70% in the stacking direction. Unlike other liquid-crystal tuning techniques where a pregenerated structure is infiltrated, this optical tuning method is a one-step process that allows arbitrary structures to be written into a solid liquid-crystal-polymer composite and leads to a high dielectric contrast.
Unraveling a role for dopamine in Huntington's disease: The dual role of reactive oxygen species and D2 receptor stimulation
Authors: Charvin Delphine , Vanhoutte Peter , Pagès Christiane , Borelli Emiliana , Caboche Jocelyne
Published: August 2005

Huntington's disease (HD), an inherited neurodegenerative disorder, results from an abnormal polyglutamine extension in the N-terminal region of the huntingtin protein. This mutation leads to protein aggregation and neurotoxicity. Despite its widespread expression in the brain and body, mutated huntingtin causes selective degeneration of striatal projection neurons. In the present study, we investigate the role of dopamine (DA) in this preferential vulnerability. Using primary cultures of striatal neurons transiently expressing GFP-tagged-exon 1 of mutated huntingtin, we show that low doses of DA (100 μM) act synergistically with mutated huntingtin to activate the proapoptotic transcription factor c-Jun. Surprisingly, DA also increases aggregate formation of mutated huntingtin in all cellular compartments, including neurites, soma, and nuclei. DA-dependent potentiation of c-Jun activation was reversed by ascorbate, a reactive oxygen species (ROS) scavenger, and SP-600125, a selective inhibitor of the c-Jun N-terminal kinase (JNK) pathway. By contrast, DA effects on aggregate formation were reversed by a selective D2 receptor antagonist and reproduced by a D2 agonist. Similarly, striatal neurons from D2 knockout mice showed no effect of DA on aggregate formation. Blocking ROS production, JNK activation, or D2 receptor stimulation significantly reversed DA aggravation of mutated huntingtin-induced striatal death. The combined treatment with the ROS scavenger and D2 antagonist totally reversed DA's effects on mutated huntingtin-induced striatal death. Thus, the present results provide insights into the cellular mechanisms that govern striatal vulnerability in HD and strongly support a dual role of JNK activation and D2 receptor signaling in this process.
An ECT2–centralspindlin complex regulates the localization and function of RhoA
Authors: Yüce Özlem , Piekny Alisa , Glotzer Michael
Published: August 2005

In anaphase, the spindle dictates the site of contractile ring assembly. Assembly and ingression of the contractile ring involves activation of myosin-II and actin polymerization, which are triggered by the GTPase RhoA. In many cells, the central spindle affects division plane positioning via unknown molecular mechanisms. Here, we dissect furrow formation in human cells and show that the RhoGEF ECT2 is required for cortical localization of RhoA and contractile ring assembly. ECT2 concentrates on the central spindle by binding to centralspindlin. Depletion of the centralspindlin component MKLP1 prevents central spindle localization of ECT2; however, RhoA, F-actin, and myosin still accumulate on the equatorial cell cortex. Depletion of the other centralspindlin component, CYK-4/MgcRacGAP, prevents cortical accumulation of RhoA, F-actin, and myosin. CYK-4 and ECT2 interact, and this interaction is cell cycle regulated via ECT2 phosphorylation. Thus, central spindle localization of ECT2 assists division plane positioning and the CYK-4 subunit of centralspindlin acts upstream of RhoA to promote furrow assembly.
FAPP2 is involved in the transport of apical cargo in polarized MDCK cells
Authors: Vieira Otilia V. , Verkade Paul , Manninen Aki , Simons Kai
Published: August 2005

Phosphatidylinositol-4-phosphate (PI(4)P) is the main phosphoinositide in the Golgi complex and has been reported to play a pleiotropic role in transport of cargo from the trans-Golgi network to the plasma membrane (PM) in polarized Madin–Darby canine kidney (MDCK) cells. Overexpression of the chimeric fluorescent protein encoding the pleckstrin homology domain, which is specific for PI(4)P, inhibited both apical and basolateral transport pathways. The transport of apical cargo from the Golgi was shown to be specifically decreased by adenovirus-mediated RNA interference directed against PI(4)P adaptor protein (FAPP) 2. FAPP1 depletion had no effect on transport. On the other hand, FAPP2 was not involved in the Golgi-to-PM transport of cargo that was targeted to the basolateral membrane domain. Thus, we conclude that FAPP2 plays a specific role in apical transport in MDCK cells.
Reaching out for signals
Authors: Lidke Diane S. , Lidke Keith A. , Rieger Bernd , Jovin Thomas M. , Arndt-Jovin Donna J.
Published: August 2005

ErbB1 receptors situated on cellular filopodia undergo systematic retrograde transport after binding of the epidermal growth factor (EGF) and activation of the receptor tyrosine kinase. Specific inhibitors of the erbB1 receptor tyrosine kinase as well as cytochalasin D, a disruptor of the actin cytoskeleton, abolish transport but not free diffusion of the receptor–ligand complex. Diffusion constants and transport rates were determined with single molecule sensitivity by tracking receptors labeled with EGF conjugated to fluorescent quantum dots. Retrograde transport precedes receptor endocytosis, which occurs at the base of the filopodia. Initiation of transport requires the interaction and concerted activation of at least two liganded receptors and proceeds at a constant rate mediated by association with actin. These findings suggest a mechanism by which filopodia detect the presence and concentration of effector molecules far from the cell body and mediate cellular responses via directed transport of activated receptors.
An enzymatic cascade of Rab5 effectors regulates phosphoinositide turnover in the endocytic pathway
Authors: Shin Hye-Won , Hayashi Mitsuko , Christoforidis Savvas , Lacas-Gervais Sandra , Hoepfner Sebastian , Wenk Markus R. , Modregger Jan , Uttenweiler-Joseph Sandrine , Wilm Matthias , Nystuen Arne , Frankel Wayne N. , Solimena Michele , De Camilli Pietro , Zerial Marino
Published: August 2005

Generation and turnover of phosphoinositides (PIs) must be coordinated in a spatial- and temporal-restricted manner. The small GTPase Rab5 interacts with two PI 3-kinases, Vps34 and PI3Kβ, suggesting that it regulates the production of 3-PIs at various stages of the early endocytic pathway. Here, we discovered that Rab5 also interacts directly with PI 5- and PI 4-phosphatases and stimulates their activity. Rab5 regulates the production of phosphatidylinositol 3-phosphate (PtdIns[3]P) through a dual mechanism, by directly phosphorylating phosphatidylinositol via Vps34 and by a hierarchical enzymatic cascade of phosphoinositide-3-kinaseβ (PI3Kβ), PI 5-, and PI 4-phosphatases. The functional importance of such an enzymatic pathway is demonstrated by the inhibition of transferrin uptake upon silencing of PI 4-phosphatase and studies in weeble mutant mice, where deficiency of PI 4-phosphatase causes an increase of PtdIns(3,4)P2 and a reduction in PtdIns(3)P. Activation of PI 3-kinase at the plasma membrane is accompanied by the recruitment of Rab5, PI 4-, and PI 5-phosphatases to the cell cortex. Our data provide the first evidence for a dual role of a Rab GTPase in regulating both generation and turnover of PIs via PI kinases and phosphatases to coordinate signaling functions with organelle homeostasis.
Spontaneous atopic dermatitis in mice expressing an inducible thymic stromal lymphopoietin transgene specifically in the skin
Authors: Yoo Jane , Omori Miyuki , Gyarmati Dora , Zhou Baohua , Aye Theingi , Brewer Avery , Comeau Michael R. , Campbell Daniel J. , Ziegler Steven F.
Published: August 2005

The cytokine thymic stromal lymphopoietin (TSLP) has recently been implicated in the pathogenesis of atopic dermatitis (AD) and other allergic diseases in humans. To further characterize its role in this disease process, transgenic mice were generated that express a keratinocyte-specific, tetracycline-inducible TSLP transgene. Skin-specific overexpression of TSLP resulted in an AD-like phenotype, with the development of eczematous lesions containing inflammatory dermal cellular infiltrates, a dramatic increase in Th2 CD4+ T cells expressing cutaneous homing receptors, and elevated serum levels of IgE. These transgenic mice demonstrate that TSLP can initiate a cascade of allergic inflammation in the skin and provide a valuable animal model for future study of this common disease.
Possible role of human herpesvirus 8 in the lymphoproliferative disorders in common variable immunodeficiency
Authors: Wheat William H. , Cool Carlyne D. , Morimoto Yoshikazu , Rai Pradeep R. , Kirkpatrick Charles H. , Lindenbaum Barbara A. , Bates Christopher A. , Ellison Misoo C. , Serls Amanda E. , Brown Kevin K. , Routes John M.
Published: August 2005

Patients who have common variable immunodeficiency (CVID) and granulomatous/lymphocytic interstitial lung disease (GLILD) are at high risk for early mortality and B cell lymphomas. Infection with human herpes virus type 8 (HHV8), a B cell lymphotrophic virus, is linked to lymphoproliferative disorders in people who have secondary immunodeficiencies. Therefore, we determined the prevalence of HHV8 infection in CVID patients with GLILD. Genomic DNA isolated from peripheral blood mononuclear cells was screened by nested- and real time-quantitative PCR (QRT-PCR) for the presence of HHV8 genome. It was positive in 6/9 CVID patients with GLILD (CVID-GLILD), 1/21 CVID patients without GLILD (CVID-control), and no patients receiving intravenous gamma globulin (n = 13) or normal blood donors (n = 20). Immunohistochemistry (IHC) demonstrated expression of the latency-associated nuclear antigen-1 (LANA-1) in the biopsies of the lung, liver, and bone marrow of four patients with CVID-GLILD. One CVID-GLILD patient developed a B cell lymphoma during the course of the study. QRT-PCR demonstrated high copy number of HHV8 genome and IHC showed diffuse staining for LANA-1 in the malignant lymph node. HHV8 infection may be an important factor in the pathogenesis of the interstitial lung disease and lymphoproliferative disorders in patients with CVID.
XBP-1 specifically promotes IgM synthesis and secretion, but is dispensable for degradation of glycoproteins in primary B cells
Authors: Tirosh Boaz , Iwakoshi Neal N. , Glimcher Laurie H. , Ploegh Hidde L.
Published: August 2005

Differentiation of B cells into plasma cells requires X-box binding protein–1 (XBP-1). In the absence of XBP-1, B cells develop normally, but very little immunoglobulin is secreted. XBP-1 controls the expression of a large set of genes whose products participate in expansion of the endoplasmic reticulum (ER) and in protein trafficking. We define a new role for XBP-1 in exerting selective translational control over high and sustained levels of immunoglobulin M (IgM) synthesis. XBP-1−/− and XBP-1+/+ primary B cells synthesize IgM at comparable levels at the onset of stimulation with lipopolysaccharide or CpG. However, later there is a profound depression in synthesis of IgM in XBP-1−/− B cells, notwithstanding similar levels of μmRNA. In marked contrast, lack of XBP-1 does not affect synthesis and trafficking of other glycoproteins, or of immunoglobulin light chains. Contrary to expectation, degradation of proteins from the ER, using TCRα or US11-mediated degradation of class I major histocompatibility complex molecules as substrates, is normal in XBP-1−/− B cells. Furthermore, degradation of membrane μ was unaffected by enforced expression of XBP-1. We conclude that in primary B cells, the XBP-1 pathway promotes synthesis and secretion of IgM, but does not seem to be involved in the degradation of ER proteins, including that of μ chains themselves.
Production of type I interferons
Authors: Asselin-Paturel Carine , Trinchieri Giorgio
Published: August 2005

Plasmacytoid dendritic cells (pDCs) are specialized producers of type I interferons (IFNs) that respond to most viruses. Because of their antiviral activity and regulatory functions in innate and adaptive immunity, type I IFNs are important not only for antiviral resistance but also in other types of infections and in immune pathology. Here we discuss recent data that begin to reveal the unique molecular mechanisms underlying the remarkably rapid and efficient type I IFN production by pDCs.
Control of dTTP pool size by anaphase promoting complex/cyclosome is essential for the maintenance of genetic stability
Authors: Ke Po-Yuan , Kuo Yuan-Yeh , Hu Chuan-Mei , Chang Zee-Fen
Published: August 2005

Anaphase promoting complex/cyclosome (APC/C)-mediated proteolysis is essential for chromosome segregation, mitotic exit, and G1 entry. Here, we show the importance of APC/C in the control of dTTP pool size in mammalian cells. Two enzymes, thymidine kinase 1 (TK1) and thymidylate kinase (TMPK), involved in dTTP formation are the targets of the APC/C pathway. We demonstrate that TMPK is recognized and degraded by APC/C–Cdc20/Cdh1-mediated pathways from mitosis to the early G1 phase, whereas TK1 is targeted for degradation by APC/C–Cdh1 after mitotic exit. Overexpression of wild-type TK1 and TMPK induces a four- to fivefold increase in the cellular dTTP pool without promoting spontaneous mutations in the hprt (hypoxanthine-guanine phosphoribosyl transferase) gene. In contrast, coexpression of nondegradable TK1 and TMPK expands the dTTP pool size 10-fold accompanied by a drastic dNTP pool imbalance. Most interestingly, disruption of APC/C proteolysis of TK1 and TMPK leads to growth retardation and a striking increase in gene mutation rate. We conclude that down-regulation of dTTP pool size by the APC/C pathway during mitosis and the G1 phase is an essential means to maintain a balanced dNTP pool and to avoid genetic instability.
Methylation of histone H4 by arginine methyltransferase PRMT1 is essential in vivo for many subsequent histone modifications
Authors: Huang Suming , Litt Michael , Felsenfeld Gary
Published: August 2005

PRMT1 is a histone methyltransferase that methylates Arg3 on histone H4. When we used siRNA to knock down PRMT1 in an erythroid cell line, it resulted in nearly complete loss of H4 Arg3 methylation across the chicken β-globin domain, which we use as a model system for studying the relationship of gene activity to histone modification. We observed furthermore a domain-wide loss of histone acetylation on both histones H3 and H4, as well as an increase in H3 Lys9 and Lys27 methylation, both marks associated with inactive chromatin. To determine whether the effect on acetylation was directly related to the loss of H4 Arg3 methylation, we performed an in vitro acetylation reaction on chromatin isolated from PRMT1-depleted cells. We found that nucleosomes purified from these cells, and depleted in methylation at Arg3, are readily acetylated by nuclear extracts from the same cells, if and only if the nucleosomes are incubated with PRMT1 beforehand. Thus, methylation of histones by PRMT1 was sufficient to permit subsequent acetylation. Consistent with earlier reports of experiments in vitro, H4 Arg3 methylation by PRMT1 appears to be essential in vivo for the establishment or maintenance of a wide range of “active” chromatin modifications.
The Isy1p component of the NineTeen Complex interacts with the ATPase Prp16p to regulate the fidelity of pre-mRNA splicing
Authors: Villa Tommaso , Guthrie Christine
Published: August 2005

Prp16p is a DEAH-box ATPase that transiently associates with the spliceosome to promote the structural transition required for the second chemical step. Yeast strains carrying the cold-sensitive allele prp16-302 stall the release of Prp16p at low temperatures, yet splice precursors with aberrant branchpoints at increased frequency. To identify new factors involved in the regulation of splicing fidelity, we sought suppressors of the prp16-302 growth phenotype. Deletion of the nonessential ISY1 gene (1) improves growth of prp16-302 strains, (2) alleviates stalling, and (3) restores fidelity of branchpoint usage to wild-type levels. Isy1p is a subunit of the NineTeen Complex containing Prp19p, an essential E3 ubiquitin ligase homolog required for splicing. Notably, Δisy1 PRP16 strains display reduced fidelity of 3′-splice site selection. Consistent with a recent two-state model of the spliceosome, our genetic and biochemical results suggest that Isy1p acts together with U6 snRNA to promote a spliceosomal conformation favorable for first-step chemistry. We propose that deletion of ISY1 favors the premature release of Prp16p, thus promoting second-step chemistry of precursors with inappropriate 3′-splice sites.
The growing pre-mRNA recruits actin and chromatin-modifying factors to transcriptionally active genes
Authors: Sjölinder Mikael , Björk Petra , Söderberg Emilia , Sabri Nafiseh , Östlund Farrants Ann-Kristin , Visa Neus
Published: August 2005

In the dipteran Chironomus tentans, actin binds to hrp65, a nuclear protein associated with mRNP complexes. Disruption of the actin–hrp65 interaction in vivo by the competing peptide 65-2CTS reduces transcription drastically, which suggests that the actin–hrp65 interaction is required for transcription. We show that the inhibitory effect of the 65-2CTS peptide on transcription is counteracted by trichostatin A, a drug that inhibits histone deacetylation. We also show that actin and hrp65 are associated in vivo with p2D10, an evolutionarily conserved protein with histone acetyltransferase activity that acts on histone H3. p2D10 is recruited to class II genes in a transcription-dependent manner. We show, using the Balbiani ring genes of C. tentans as a model system, that p2D10 is cotranscriptionally associated with the growing pre-mRNA. We also show that experimental disruption of the actin–hrp65 interaction by the 65-2CTS peptide in vivo results in the release of p2D10 from the transcribed genes, reduced histone H3 acetylation, and a lower level of transcription activity. Furthermore, antibodies against p2D10 inhibit run-on elongation. Our results suggest that actin, hrp65, and p2D10 are parts of a positive feedback mechanism that contributes to maintaining the active transcription state of a gene by recruiting HATs at the RNA level.