bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatially resolved ferromagnetic resonance: Imaging of ferromagnetic eigenmodes
Authors: Puzic Aleksandar , Van Waeyenberge Bartel , Chou Kang Wei , Fischer Peter , Stoll Hermann , Schütz Gisela , Tyliszczak Tolek , Rott Karsten , Brückl Hubert , Reiss Günter , Neudecker Ingo , Haug Thomas , Buess Matthias , Back Christian H.
Published: May 2005

Fast magnetization dynamics of ferromagnetic elements on sub-micron length scales is currently attracting substantial scientific interest. Studying the ferromagnetic eigenmodes in such systems provides valuable information in order to trace back the dynamical response to the underlying micromagnetic properties. The inherent time structure of third generation synchrotron sources allows for time-resolved imaging (time resolution: 70–100 ps) of magnetization dynamics at soft x-ray microscopes (lateral resolution down to 20 nm). Stroboscopic pump-and-probe experiments were performed on micron-sized Permalloy samples at a full-field magnetic transmission x-ray microscope (XM-1, beamline 6.1.2) at the ALS at Berkeley, CA. Complementary to these time-domain experiments a frequency-domain “spatially resolved ferromagnetic resonance” (SR-FMR) technique was applied to magnetic x-ray microscopy. In contrast to time-domain measurements which reflect a broadband excitation of the magnetization, the frequency-domain SR-FMR technique allows for detailed studies of specific ferromagnetic eigenmodes. First SR-FMR experiments at a scanning x-ray transmission microscope (STXM, ALS, BL 11.0.2) are reported. The sample, a 1×1μm2 Permalloy pattern, was excited by an alternating magnetic field with a frequency of 250 MHz. By varying the phase relation between the sine excitation and the x-ray flashes of the synchrotron, the dynamics of a vortex motion eigenmode was investigated in time and space.
Superexchange and iron valence control by off-stoichiometry in yttrium iron garnet thin films grown by pulsed laser deposition
Authors: Dumont Y. , Keller N. , Popova E. , Schmool D. S. , Bhattacharya S. , Stahl B. , Tessier M. , Guyot M.
Published: May 2005

Controlled off-stoichiometric single phase polycrystalline yttrium iron garnet (YIG) thin films have been grown by pulsed laser deposition, adjusting the oxygen partial pressure PO2 between 5 and 400 mTorr. Atomic stoichiometry by RBS shows an oxygen deficiency for PO2Pstoich. Pstoich=30mTorr refers to films showing magnetic and structural properties of the bulk stoichiometric YIG. Curie temperature Tc and saturation magnetization 4πMs decreased for PO2Pstoich: Increase of Tc (up to +10%) and of 4πMs (up to +20%) and lattice parameter compression. Microscopic interpretation is given in terms of superexchange interaction and creation and site selectivity of iron vacancies.
Iron nitride nanoparticles by nanocluster deposition
Authors: Xu Yun-Hao , Hosein Sean , Judy Jack H. , Wang Jian-Ping
Published: May 2005

Fe 16 N 2 has been reported to have a saturation magnetization as high as 2.8–3.0T based on molecular beam epitaxy deposited single crystal film. We report on Fe nitride nanoparticles prepared with a gas-aggregation nanocluster deposition technique, which could potentially generate pure metastable Fe16N2 phase nanoparticles. Nitrogen gas has been used to nitride the particles after they have been formed in the cluster source. X-ray diffraction patterns show a peak split of α-Fe (110) at 52.4° (2θ), which indicates the formation of Fe3N phase.
Crystallite size dependence of natural resonance frequency for spin-sprayed Fe3O4∕γ–Fe2O3 films highly permeable up to gigahertz range
Authors: Tada Masaru , Abe Tatsunobu , Miyasaka Jin , Matsushita Nobuhiro , Abe Masanori
Published: May 2005

We successfully prepared Fe3O4∕γ–Fe2O3 polycrystalline films having a wide range of crystallite sizes by changing the plating conditions at 90°C. The films had lattice constants (determined by x-ray diffraction) independent of the crystallite size D within our experimental error. Natural resonance frequency fr for the film increased from 0.8to1.9GHz as the crystallite size D decreased from 63to30nm. In our polycrystalline films, magnetic anisotropy field Hk is induced mainly by crystallite boundary/surface effect so that a larger crystallite will cause a weaker Hk. Those Fe3O4∕γ–Fe2O3 films are also promising to be used in conducted noise suppressors operated in a gigahertz range.
Review of progress in Fast Ignition
Authors: Tabak M. , Clark D. S. , Hatchett S. P. , Key M. H. , Lasinski B. F. , Snavely R. A. , Wilks S. C. , Town R. P. J. , Stephens R. , Campbell E. M. , Kodama R. , Mima K. , Tanaka K. A. , Atzeni S. , Freeman R.
Published: May 2005

Marshall Rosenbluth’s extensive contributions included seminal analysis of the physics of the laser-plasma interaction and review and advocacy of the inertial fusion program. Over the last decade he avidly followed the efforts of many scientists around the world who have studied Fast Ignition, an alternate form of inertial fusion. In this scheme, the fuel is first compressed by a conventional inertial confinement fusion driver and then ignited by a short (∼10ps) pulse, high-power laser. Due to technological advances, such short-pulse lasers can focus power equivalent to that produced by the hydrodynamic stagnation of conventional inertial fusion capsules. This review will discuss the ignition requirements and gain curves starting from simple models and then describe how these are modified, as more detailed physics understanding is included. The critical design issues revolve around two questions: How can the compressed fuel be efficiently assembled? And how can power from the driver be delivered efficiently to the ignition region? Schemes to shorten the distance between the critical surface where the ignitor laser energy is nominally deposited and the ignition region will de discussed. The current status of Fast Ignition research is compared with our requirements for success. Future research directions will also be outlined.
A wave-packet simulation of the low-lying singlet electronic transitions of acetylene
Authors: Schubert Bernd , Köppel Horst , Lischka Hans
Published: May 2005

The vibronic structure of the S0→S1 and the S0→S2 electronic transitions of acetylene is studied theoretically based on an ab initio quantum-dynamical approach. The underlying potential-energy surfaces and transition dipole moment functions are obtained from high-level multireference calculations, including the Davidson correction. Ensuing quantum-dynamical simulations rely on the wave-packet propagation method, using grid techniques, and including three nuclear degrees of freedom (C–C stretching and both HCC bending modes for J=0). The importance of strong anharmonicity is assessed, especially for the S2 excited state with its unusual potential-energy surface. Good overall agreement with the experimental UV absorption spectrum of acetylene is achieved in the range of 6–8 eV.
Design, simulation, and application of quasi-spherical 100ns z-pinch implosions driven by tens of mega-amperes
Authors: Nash T. J. , McDaniel D. H. , Leeper R. J. , Deeney C. D. , Sanford T. W. L. , Struve K. , DeGroot J. S.
Published: May 2005

A quasi-spherical z-pinch may directly compress foam or deuterium and tritium in three dimensions as opposed to a cylindrical z-pinch, which compresses an internal load in two dimensions only. Because of compression in three dimensions the quasi-spherical z-pinch is more efficient at doing pdV work on an internal fluid than a cylindrical pinch. Designs of quasi-spherical z-pinch loads for the 28MA 100ns driver ZR, results from zero-dimensional (0D) circuit models of quasi-spherical implosions, and results from 1D hydrodynamic simulations of quasi-spherical implosions heating internal fluids will be presented. Applications of the quasi-spherical z-pinch implosions include a high radiation temperature source for radiation driven experiments, a source of neutrons for treating radioactive waste, and a source of fusion energy for a power generator.
First-principles investigations of the polarizability of small-sized and intermediate-sized copper clusters
Authors: Yang Mingli , Jackson Koblar A.
Published: May 2005

Density functional theory calculations are used to compute the dipole polarizabilities of copper clusters. Structures for the clusters are taken from the literature for n=2–32 and several isomers are used for each cluster size for n⩽10. The calculated polarizabilities are in good agreement with the prediction of a simple jellium model, but much smaller than experimental observations for n=9–32 [M. B. Knickelbein, J. Chem. Phys., 120, 10450 (2004)]. To investigate this difference, the calculated polarizabilities are tested for the effects of basis set, electron correlation, and equilibrium geometry for small-size clusters (n=2–10). These effects are too small to account for the theory-experiment gap. Temperature effects are also studied. Thermal expansion of the clusters leads to very small changes in polarizability. On the other hand, the presence of permanent dipoles in the clusters could account for the experimental observations if the rotational temperature of the clusters were sufficiently low. The potential importance of the cluster dipole moments implies that reliable ground-state structures and experimental temperatures are needed to find quantitative agreement between calculated and observed polarizabilities.
Energy of charged states in the RDX crystal: Trapping of charge-transfer pairs as a possible mechanism for initiating detonation
Authors: Tsiaousis D. , Munn R. W.
Published: May 2005

Calculations for the crystalline energetic material RDX (1,3,5-trinitro-1,3,5-triazacyclohexane) yield the effective polarizability (17.2Å3), local electric field tensor, effective dipole moment (9.40 D), and dipole-dipole energy (−27.2kJ∕mol). Fourier-transform techniques give the polarization energy P for a single charge in the perfect crystal as −1.14eV; the charge-dipole energy WD is zero if the crystal carries no bulk dipole moment. Polarization energies for charge-transfer (CT) pairs combine with the Coulomb energy EC to give the screened Coulomb energy Escr; screening is nearly isotropic with Escr≈EC∕2.6. For CT pairs WD reduces to a term δWD arising from the interaction of the charge on each ion with the change in dipole moment on the other ion relative to the neutral molecule. The dipole moments are calculated as 7.40 D for the neutral molecule and 6.84 D and 7.44 D for the anion and cation, giving the lowest two CT pairs at −1.34eV and −0.94eV. The changes in P and WD near a molecular vacancy yield traps with depths that reach 400 meV for single charges and 185 meV for the nearest-neighbor CT pair. Divacancies yield traps with depths nearly equal to the sum of those produced by the separate vacancies. These results are consistent with a mechanism in which detonation of RDX is initiated by mechanical generation of CT pairs that localize at vacancies, recombine, and release energy sufficient to break bonds; crystals of molecules with lower dipole moments should be less sensitive.
Potential surfaces and dynamics of the O(P3)+H2O(XA111)→OH(XΠ2)+OH(XΠ2) reaction
Authors: Braunstein M. , Panfili R. , Shroll R. , Bernstein L.
Published: May 2005

We present global potential energy surfaces for the three lowest triplet states in O(P3)+H2O(XA11) collisions and present results of classical dynamics calculations on the O(P3)+H2O(XA11)→OH(XΠ2)+OH(XΠ2) reaction using these surfaces. The surfaces are spline-based fits of ∼20000 fixed geometry ab initio calculations at the complete-active-space self-consistent field+second-order perturbation theory (CASSCF+MP2) level with a O(4s3p2d1f)/H(3s2p) one electron basis set. Computed rate constants compare well to measurements in the 1000–2500 K range using these surfaces. We also compute the total, rovibrationally resolved, and differential angular cross sections at fixed collision velocities from near threshold at ∼4kms−1 (16.9kcalmol−1 collision energy) to 11kms−1 (122.5kcalmol−1 collision energy), and we compare these computed cross sections to available space-based and laboratory data. A major finding of the present work is that above ∼40kcalmol−1 collision energy rovibrationally excited OH(XΠ2) products are a significant and perhaps dominant contributor to the observed 1–5 μ spectral emission from O(P3)+H2O(XA11) collisions. Another important result is that OH(XΠ2) products are formed in two distinct rovibrational distributions. The “active” OH products are formed with the reagent O atom, and their rovibrational distributions are extremely hot. The remaining “spectator” OH is relatively rovibrationally cold. For the active OH, rotational energy is dominant at all collision velocities, but the opposite holds for the spectator OH. Summed over both OH products, below ∼50kcalmol−1 collision energy, vibration dominates the OH internal energy, and above ∼50kcalmol−1 rotation is greater than vibrational energy. As the collision energy increases, energy is diverted from vibration to mostly translational energy. We note that the present fitted surfaces can also be used to investigate direct collisional excitation of H2O(XA11) by O(P3) and also OH(XΠ2)+OH(XΠ2) collisions.
Photoionization dynamics of glycine adsorbed on a silicon cluster: “On-the-fly” simulations
Authors: Shemesh Dorit , Baer Roi , Seideman Tamar , Gerber R. Benny
Published: May 2005

Dynamics of glycine chemisorbed on the surface of a silicon cluster is studied for a process that involves single-photon ionization, followed by recombination with the electron after a selected time delay. The process is studied by “on-the-fly” molecular dynamics simulations, using the semiempirical parametric method number 3 (PM3) potential energy surface. The system is taken to be in the ground state prior to photoionization, and time delays from 5 to 50 fs before the recombination are considered. The time evolution is computed over 10 ps. The main findings are (1) the positive charge after ionization is initially mostly distributed on the silicon cluster. (2) After ionization the major structural changes are on the silicon cluster. These include Si–Si bond breaking and formation and hydrogen transfer between different silicon atoms. (3) The transient ionization event gives rise to dynamical behavior that depends sensitively on the ion state lifetime. Subsequent to 45 fs evolution in the charged state, the glycine molecule starts to rotate on the silicon cluster. Implications of the results to various processes that are induced by transient transition to a charged state are discussed. These include inelastic tunneling in molecular devices, photochemistry on conducting surfaces, and electron-molecule scattering.
Signatures of the hydrogen bonding in the infrared bands of water
Authors: Brubach J.-B. , Mermet A. , Filabozzi A. , Gerschel A. , Roy P.
Published: May 2005

Infrared spectroscopy measurements have been completed over a wide range of frequencies allowing to measure the evolution of both intramolecular and intermolecular vibrational modes in water as a function of temperature. Emphasis is made on the high frequency OH stretching band and the so-called connectivity band that lies in the far infrared region. The substructures of the two infrared bands are analyzed in terms of different levels of connectivity of the water molecules, along the statements of the percolation model. Both band profiles appear to be related to the different degrees of connectivity of water molecules. Comparison of the data with the predictions of the percolation model shows good agreement as for the temperature evolution of liquid water. This work provides additional support to the interpretation of water bands substructures as signatures of its very specific connectivity pattern.
Investigation of the spectra of phosphorescent organic light-emitting devices in relation to emission zone
Authors: Wu Zhaoxin , Wang Liduo , Lei Gangtie , Qiu Yong
Published: May 2005

The dependence of the electroluminescent spectra on the emission zone of blue electrophosphorscent light emitting diodes (PHOLEDs) was investigated. The light emission of a PHOLED was tuned from blue to greenish blue by adjusting the position of the emission zone in the PHOLED. Experimental results agreed well with the numerical simulation based on the effect of the wide-angle optical interference by the metal cathode. The comparison of the numerical results and the electroluminescent spectra of the PHOLED was then extended to serve as the basis of another method to determine the location of the emission zones of PHOLEDs.
Optically pumped terahertz laser based on intersubband transitions in a GaN∕AlGaN double quantum well
Authors: Vukmirović N. , Jovanović V. D. , Indjin D. , Ikonić Z. , Harrison P. , Milanović V.
Published: May 2005

A design for a GaN∕AlGaN optically pumped terahertz laser emitting at 34 μm (ΔE∼36meV) is presented. This laser uses a simple three-level scheme where the depopulation of the lower laser level is achieved via resonant longitudinal-optical-phonon emission. The quasibound energies and associated wave functions are calculated with the intrinsic electric field induced by the piezoelectric and the spontaneous polarizations. The structures based on a double quantum well were simulated and the output characteristics extracted using a fully self-consistent rate equation model with all relevant scattering processes included. Both electron-longitudinal-optical phonon and electron-acoustic-phonon interactions were taken into account. The carrier distribution in subbands was assumed to be Fermi–Dirac-like, with electron temperature equal to the lattice temperature, but with different Fermi levels for each subband. A population inversion of 12% for a pumping flux Φ=1027cm−2s−1 at room temperature was calculated for the optimized structure. By comparing the calculated modal gain and estimated waveguide and mirror losses the feasibility of laser action up to room temperature is predicted.
Influence of dipolar interaction on small magnetic dot arrays
Authors: Zhang L. F. , Xu C. , Hui P. M. , Ma Y. Q.
Published: May 2005

The effects of dipolar interaction in an array of small magnetic dots with perpendicular anisotropy are studied numerically within the framework of the Landau–Lifshitz–Gilbert equation. In the absence of a magnetic field, three typical configurations of the magnetic moments are found, depending on the dipolar coupling strength. Magnetization processes both parallel and perpendicular to the array are studied. The hysteresis loops are found to be highly sensitive to the dipolar coupling strength. The in-plane hysteresis loops are dominated by the strong dipolar interaction between particles, while the out-of-plane hysteresis loops are dominated by the perpendicular anisotropy. The coercive field, saturation field, and remanence are also sensitive to the strength of dipolar interaction. Dipole interactions also affect the characteristic switching time in a coupled array. Depending on the packing density of the dots in an array, the switching time may be shortened or lengthened.
Reconstruction of universal Drinfeld twists from representations
Authors: Blohmann Christian
Published: May 2005

Universal Drinfeld twists are inner automorphisms which relate the coproduct of a quantum enveloping algebra to the coproduct of the undeformed enveloping algebra. Even though they govern the deformation theory of classical symmetries and have appeared in numerous applications, no twist for a semisimple quantum enveloping algebra has ever been computed. It is argued that universal twists can be reconstructed from their well-known representations. A method to reconstruct an arbitrary element of the enveloping algebra from its irreducible representations is developed. For the twist this yields an algebra valued generating function to all orders in the deformation parameter, expressed by a combination of basic and ordinary hypergeometric functions. It is shown how the generating function can be expanded to the formal power series of the twist. An explicit expression for the universal twist of su(2) is given up to third order.
Nanoscale imaging of surface acoustic waves by scanning tunneling microscopy
Authors: Koch R. , Yang Jianshu
Published: May 2005

The scanning tunneling microscope (STM) has proven to be a powerful technique for probing surface acoustic waves (SAWs) with high spatial resolution. Here we use our ultrahigh-vacuum SAW-STM to investigate a Rayleigh wave excited in LiNbO3 with emphasis laid on the SAW-induced signals at steps that are only a few atomic layers high. Our study reveals that on the length scale of a few nanometer the description of the amplitude and phase contrast by a plain geometrical model fails and a variety of other mechanisms decisively affect the SAW-induced signal. At steps the lateral surface movement due to the SAW may play an important role. For larger step inclination angles also the shape of the STM tip as well as tip-surface interactions become relevant, which may even drive a SAW-induced movement of the tip apex.
Fragmentation dynamics of fullerenes in intense femtosecond-laser fields: Loss of small neutral fragments on a picosecond time scale
Authors: Boyle M. , Laarmann T. , Shchatsinin I. , Schulz C. P. , Hertel I. V.
Published: May 2005

The fragmentation dynamics of C60 irradiated with intense femtosecond laser pulses is studied with one-color pump-probe spectroscopy. Small neutral fragments (C, C2, and C3) are formed by an 800-nm pump pulse which are then postionized by a delayed probe pulse. The respective ion signals detected by the time-of-flight mass spectrometry dramatically increase on a time scale of 10–20ps.
Properties of low and medium frequency modes in two-fluid plasma
Authors: Ishida Akio , Cheng C. Z. , Peng Y-K. M.
Published: May 2005

Based on a two-fluid plasma model where the electron mass and the displacement current are neglected, the eigenmode properties such as the frequency and the compressibility are studied. It is found that these properties strongly depend on the two-fluid parameter kℓi, where k is the wave number of a mode and ℓi is the ion skin depth. Especially it is found that as the two-fluid parameter kℓi increases beyond unity, the Alfvén wave, which is an incompressible mode in the magnetohydrodynamics (MHD) limit, becomes compressible and its phase velocity approaches to the acoustic speed. The slow magnetosonic wave, which is compressible in the MHD limit, becomes incompressible as kℓi increases. Implications of these results are also discussed.
Asymmetric magnetization reversal in exchange-biased NiFe∕CoO submicron-sized structures
Authors: Girgis E. , Portugal R. D. , Van Bael M. J. , Temst K. , Van Haesendonck C.
Published: May 2005

Exchange coupling in patterned exchange-biased NiFe∕CoO squares with different sizes has been studied. Arrays of square dots with the lateral size varying between 300 and 900nm and a fixed interdot distance of 800nm were prepared by sputtering followed by in situ oxidation. Exchange bias in the initial and trained loops was studied as a function of the size, temperature, and cooling field. A decrease in the exchange bias shift was observed with a decreasing size, which might be due to the magnetostatic interdots interaction. For the trained loops, a variation of exchange bias with the temperature and cooling field, similar to those observed in continuous films, was observed.
Deep trapping of electrons by oblique shock waves
Authors: Zindo Atsushi , Ohsawa Yukiharu , Bessho Naoki , Sydora Richard
Published: May 2005

The mechanism of electron trapping by an oblique shock wave is studied with theory and particle simulations. An energy equation is derived, which focuses on particle velocity and electric field parallel to the magnetic field B. It is then shown that electrons can be reflected by a negative dip of F, where F is the integral of the parallel electric field, E‖=(E∙B)∕B, along B. The parallel energy is decreased after the reflection owing to the recovery of F to positive values. This leads to deep electron trapping. These theoretical predictions are verified with relativistic, electromagnetic particle simulations.
Direct numerical simulation of two opposing wall jets
Authors: Johansson Peter S. , Andersson Helge I.
Published: May 2005

Two opposing plane turbulent jet flows along a planar surface interact severely in the collision zone above the stagnation point and thereafter form a plane fountainlike merged jet perpendicular to the surface. Direct numerical simulations have been performed to explore the physics of the turbulence field in the collision zone and in the fountain jet formed as a merger of the two originally countercurrent jet streams. It is observed that the turbulence level is exceptionally high in the collision zone, i.e., just above the high-pressure stagnation region. This is ascribed to excess mean shear production arising from the streamline curvature of the bending jets. The turbulence is therefore far from equilibrium and the kinetic energy production exceeds its dissipation rate by a factor of 3. Mean-velocity profiles and second-order moments in the fountain jet compare well with measured data in similar flows. The growth rate of the fountain jet is about 0.15, which is 50% higher than the spreading rate of a conventional plane jet. Several physical aspects of this flow are hard to accommodate in Reynolds-averaged Navier–Stokes-based turbulence models. To facilitate the strive towards better turbulence closures, data fields for all terms in the kinetic energy budget are provided in this paper.
Two-equation modeling of turbulent rotating flows
Authors: Cazalbou J.-B. , Chassaing P. , Dufour G. , Carbonneau X.
Published: May 2005

The possibility to take into account the effects of the Coriolis acceleration on turbulence is examined in the framework of two-equation eddy-viscosity models. General results on the physical consistency of such turbulence models are derived from a dynamical-system approach to situations of time-evolving homogeneous turbulence in a rotating frame. Application of this analysis to a (k,ϵ) model fitted with an existing Coriolis correction [J. H. G. Howard, S. V. Patankar, and R. M. Bordynuik, “Flow prediction in rotating ducts using Coriolis-modified turbulence models,” ASME Trans. J. Fluids Eng. 102, 456 (1980)] is performed. Full analytical solutions are given for the flow predicted with this model in the situation of homogeneously sheared turbulence subject to rotation. The existence of an unphysical phenomenon of blowup at finite time is demonstrated in some range of the rotation-to-shear ratio. A direct connection is made between the slope of the mean-velocity profile in the plane-channel flow with spanwise rotation, and a particular fixed point of the dynamical system in homogeneously sheared turbulence subject to rotation. The general analysis, and the understanding of typical inaccuracies and misbehavior observed with the existing model, are then used to design a new model which is free from the phenomenon of blowup at finite time and able to account for both of the main influences of rotation on turbulence: the inhibition of the spectral transfer to high wave numbers and the shear/Coriolis instability.
Axisymmetric Stokes flow through a circular orifice in a tube
Authors: Jeong Jae-Tack , Choi Sung-Ryul
Published: May 2005

Axisymmetric Stokes flow through a circular tube with a thin orifice inside is investigated. At far upstream and downstream from the orifice, the Hagen–Poiseuille flow exists in the tube. The problem is investigated by considering Stokes equation analytically using a complex eigenfunction. Flow properties such as stream function and pressure distribution are determined. From the results, the streamline pattern and pressure distribution are drawn. The excess pressure drop due to the orifice and the force exerted on the orifice are calculated as functions of the radius of the orifice.
Properties of 6H–SiC crystals grown by hydrogen-assisted physical vapor transport
Authors: Li Q. , Polyakov A. Y. , Skowronski M. , Fanton M. A. , Cavalero R. C. , Ray R. G. , Weiland B. E.
Published: May 2005

Effects of hydrogen addition to the growth ambient during physical vapor transport (PVT) growth of 6H–SiC were investigated using secondary ion mass spectrometry, deep level transient spectroscopy, and Hall effect measurement. The background nitrogen concentration and the free electron density decrease with increasing hydrogen content. The formation of electron traps (activation energies of 0.4eV, 0.6eV, 0.7eV, 0.9eV, and 1eV) was also strongly suppressed. The above results are interpreted as a consequence of hydrocarbon formation produced by the reaction of hydrogen with the SiC source and the graphite parts of the furnace. This leads to more congruent evaporation of SiC and the shift of the gas phase and the SiC deposit stoichiometry due to less Si-rich conditions than in standard PVT growth.
Recombination distribution and color tuning of multilayer organic light-emitting diode
Authors: Chen Chia-Hsun , Meng Hsin-Fei
Published: May 2005

The recombination distribution of an organic light-emitting diode with multiple emissive layers is studied theoretically. Due to the relatively low electron mobility, the recombination concentrates in the layer next to the cathode. As the voltage increases, the recombination extends to the subsequent layers because the electric field strongly enhances the electron mobility. Assume that the layers are arranged in the order of red, green, blue, and electron blocking from the cathode, the emission color can be continuously tuned by the voltage over a wide range. Taking typical material parameters and emission spectra for the layers, we show that Commission Internationale de L’Eclairage coordinate can move from (0.5,0.5) (orange) to (0.3,0.5) (green) to (0.2,0.3) (blue) as the voltage increases from 3to13V. The ratio between the electron and hole mobilities of the green layer and the electron barrier between green and blue layers is found to be crucial for the wide range of color tunability.
Morphotropic phase boundary in epitaxial Pb(Zr,Ti)O3 thin films: Two-dimensional planar size effect
Authors: Lee Kilho , Baik Sunggi
Published: May 2005

The epitaxial Pb(Zr,Ti)O3 (PZT) thin films were patterned into small islands by a photolithographic process, and the morphotropic phase boundary (MPB) in which the tetragonal and rhombohedral phases coexist was realized by changing the two-dimensional planar sizes. The MPB moved toward the Zr-rich composition due to two-dimensional film stress in the continuous epitaxial PZT thin films. The 600-nm-thick epitaxial Pb(Zr0.55Ti0.45)O3 and Pb(Zr0.60Ti0.40)O3 films were found highly rich in tetragonal phase. As the films were patterned progressively in smaller sizes and the misfit strains were relaxed further accordingly, the MPB was restored to the original bulk composition, showing higher fractions of rhombohedral phase. In the epitaxial Pb(Zr0.55Ti0.45)O3 film, two-dimensional patterns of 100×100, 10×10, and 5×5μm2 were found within the MPB region, whereas the smallest 2×2μm2 patterns were fully rhombohedral. On the other hand, in the epitaxial Pb(Zr0.60Ti0.40)O3 film, only the 100×100μm2 patterns belonged to MPB rich in tetragonal phase, while the smaller patterns exhibited fully rhombohedral phases.
Optical evidence for lack of polarization in (112¯0) oriented GaN∕(AlGa)N quantum structures
Authors: Akopian N. , Bahir G. , Gershoni D. , Craven M. D. , Speck J. S. , DenBaars S. P.
Published: May 2005

We apply continuous and time resolved photoluminescence spectroscopy for studying GaN∕AlGaN multiquantum wells structures grown on nonpolar a-plane GaN templates. We found that (a) the energy of the emission from the nonpolar samples decreases slightly with the quantum well width, in a manner explained by the quantum size effect only; (b) the energy differences between the absorption and the emission peaks are independent of the well width; and (c) the decay time of the photoluminescence is only slightly dependent on the quantum well width and is quite similar to that of bulk GaN. These observations are markedly different from measurements obtained from conventional polar [0001] oriented quantum well samples. They clearly demonstrate the absence of an electric field in the nonpolar samples. Our observations are favorably compared with an eight bands k∙P model calculations.
Natalignathus, gen. nov. and larvae of Atanygnathus: a missing phylogenetic link between subtribes Quediina and Tanygnathinina (Coleoptera:Staphylinidae:Staphylininae:Staphylinini)
Authors: Solodovnikov A. Yu.
Published: May 2005

Discovery of adults and a larva of Natalignathus, a new South African endemic genus, and examination of previously undescribed larvae of Atanygnathus Jakobson shed light on the phylogenetic relationships of the puzzling rove beetle subtribe Tanygnathinina (Staphylinidae : Staphylininae : Staphylinini). Based on plesiomorphic states for many characters of Natalignathus, gen. nov., inferred on the basis of comparison of the new genus with Atanygnathus, various Quediina and other Staphylinini, Natalignathus can be considered either a relatively plesiomorphy-rich member of Tanygnathinina, or a derived genus of Quediina, essentially linking these two subtribes together. Based on morphological and distributional data, it is preliminarily assumed that Atanygnathus evolved from some lineage of southern Quediina, which currently are very poorly known. Comparative study of the adults of Natalignathus and Atanygnathus allows correction of earlier misinterpretations of the structure of the aedeagus and head capsule ridges of Atanygnathus. Detailed morphological descriptions are provided for adults and a larva of Natalignathus and for the larvae of two species of Atanygnathus, A. bicolor (Casey) and A. sp. 1. Special appendages of unknown function are present on the mesothoracic spiracles of the examined larvae of Atanygnathus. No similar structures are known in any other group of Staphylinidae or Coleoptera. Based on the new findings, a review of the state of knowledge of the subtribes Quediina and Tanygnathinina and an updated diagnosis of the latter are provided.
The glucocorticoid receptor blocks P-TEFb recruitment by NFκB to effect promoter-specific transcriptional repression
Authors: Luecke Hans F. , Yamamoto Keith R.
Published: May 2005

To investigate the determinants of promoter-specific gene regulation by the glucocorticoid receptor (GR), we compared the composition and function of regulatory complexes at two NFκB-responsive genes that are differentially regulated by GR. Transcription of the IL-8 and IκBα genes is stimulated by TNFα in A549 cells, but GR selectively represses IL-8 mRNA synthesis by inhibiting Ser2 phosphorylation of the RNA polymerase II (pol II) C-terminal domain (CTD). The proximal κB elements at these genes differ in sequence by a single base pair, and both recruited RelA and p50. Surprisingly, GR was recruited to both of these elements, despite the fact that GR failed to repress the IκBα promoter. Rather, the regulatory complexes formed at IL-8 and IκBα were distinguished by differential recruitment of the Ser2 CTD kinase, P-TEFb. Disruption of P-TEFb function by the Cdk-inhibitor, DRB, or by small interfering RNA selectively blocked TNFα stimulation of IL-8 mRNA production. GR competed with P-TEFb recruitment to the IL-8 promoter. Strikingly, IL-8 mRNA synthesis was repressed by GR at a post-initiation step, demonstrating that promoter proximal regulatory sequences assemble complexes that impact early and late stages of mRNA synthesis. Thus, GR accomplishes selective repression by targeting promoter-specific components of NFκB regulatory complexes.
Neural guidance molecules regulate vascular remodeling and vessel navigation
Authors: Eichmann Anne , Makinen Taija , Alitalo Kari
Published: May 2005

The development of the embryonic blood vascular and lymphatic systems requires the coordinated action of several transcription factors and growth factors that target endothelial and periendothelial cells. However, according to recent studies, the precise “wiring” of the vascular system does not occur without an ordered series of guidance decisions involving several molecules initially discovered for axons in the nervous system, including ephrins, netrins, slits, and semaphorins. Here, we summarize the new advances in our understanding of the roles of these axonal pathfinding molecules in vascular remodeling and vessel guidance, indicating that neuronal axons and vessel sprouts use common molecular mechanisms for navigation in the body.
Default neural induction: neuralization of dissociated Xenopus cells is mediated by Ras/MAPK activation
Authors: Kuroda Hiroki , Fuentealba Luis , Ikeda Atsushi , Reversade Bruno , De Robertis E.M.
Published: May 2005

Xenopus embryonic ectodermal cells dissociated for three or more hours differentiate into neural tissue instead of adopting their normal epidermal fate. This default type of neural induction occurs in the absence of Spemann's organizer signals and is thought to be caused by the dilution of endogenous BMPs into the culture medium. Unexpectedly, we observed that BMP ligands continue to signal in dissociated cells. Instead, cell dissociation induces a sustained activation of the Ras/MAPK pathway, which causes the phosphorylation of Smad1 at sites that inhibit the activity of this transcription factor. It is this activation of Ras/MAPK that is required for neuralization in dissociated ectoderm.
A novel ‘permanent’ acid‐type hair color made possible with dye–metal ion complex technology
Authors: Ochiai M. , Kawasoe T. , Yasuda M. , Harada Y. , Kimura T. , Kambe T. , Kurita J.
Published: May 2005

The advantages and disadvantages of oxidative permanent and acid‐type semi‐permanent hair colors are evident. The former provides a long‐lasting ‘permanent’ color, while the latter imparts less damage to the hair. We developed a novel acid‐type hair color technology that can allow an acid dye and a metal ion to form a complex inside the hair similar to the oxidative hair color. It is well known that acid dye diffuses into the hair and creates an ionic bond with the positively charged amino acid residues of hair protein. However, the dye can be extracted easily from the hair by daily shampooing due to the weakness of the bond. In order to strengthen this bond and to prevent the extraction of the dye by shampooing, an aluminum chloride ion was chosen as the metal ion component to form the dye–metal complex. A proper composition of penetration enhancers, benzyl alcohol and ethyl alcohol, was required to allow acid dyes to interact with the aluminum chloride ion after each component penetrates deeply into the hair to form a complex inside the hair. To provide color brightness and a color longevity effect to hair color, glycolic acid was also selected due to the observation that a weak acid with a small molecular weight would enhance those effects.
Immunoglobulin gene segment usage, location and immunogenicity in mutated and unmutated chronic lymphocytic leukaemia
Authors: Mauerer Katja , Zahrieh David , Gorgun Gullu , Li Aihong , Zhou Jianbiao , Ansén Sascha , Rassenti Laura Z. , Gribben John G.
Published: May 2005

The mutational status of the variable region of the immunoglobulin heavy chain gene (IgVH) is an important prognostic marker in B‐cell chronic lymphocytic leukaemia (B‐CLL), with mutated patients having improved outcome. To examine the impact of mutational status on VH, DH, and JH gene segment location and immunogenicity, we analysed 375 IgH sequences from 356 patients with B‐CLL. Although VH and DH gene usage was different in mutated compared to unmutated patients, there was no impact of gene location on frequency of use or clinical outcome. Surprisingly, somatic mutations did not increase the immunogenicity of the Ig, as assessed by predicted binding affinity of Ig‐derived peptides to major histocompatibility Class I and Class II molecules. Even excluding patients using VH1‐69, cases using the VH1 gene family had a poor outcome. Both mutated and unmutated CLL patients demonstrated evidence of antigen selection. The worst outcome was seen in the subset of 14 unmutated patients with similar HCDR3 amino acid sequence using VH1‐69, DH3‐3 and JH6, suggesting an antigen‐driven process modulating the clinical course.
Chimaerism analyses and subsequent immunological intervention after stem cell transplantation in patients with juvenile myelomonocytic leukaemia
Authors: Yoshimi Ayami , Niemeyer Charlotte M. , Bohmer Viktoria , Duffner Ulrich , Strahm Brigitte , Kreyenberg Hermann , Dilloo Dagmar , Zintl Felix , Claviez Alexander , Wössmann Willi , Kremens Bernhard , Holter Wolfgang , Niethammer Dietrich , Beck James F. , Kontny Udo , Nöllke Peter , Klingebiel Thomas , Bader Peter
Published: May 2005

Chimaerism analysis was performed by polymerase chain reaction amplification of short‐tandem repeat markers in 30 children following haematopoietic stem cell transplantation for juvenile myelomonocytic leukaemia (JMML). Fourteen patients always had complete chimaerism (CC); one of them relapsed after the discontinuation of the study and 13 continued in complete remission (CR). Mixed chimaerism (MC) was noted in 16 patients. Of those 12 patients demonstrated increasing MC (i‐MC); 10 relapsed and two achieved CC following discontinuation of immunosuppressive therapy (IST). Four other patients demonstrating only transient MC are alive in CR. MC with up to 20% of autologous cells could be successfully eradicated without induction of severe graft‐versus‐host disease when IST was reduced or discontinued directly after the first demonstration of MC. At the same time, MC with up to 10% of autologous cells could disappear without intervention. The interval between MC and relapse ranged from 0–320 d (median 38 d). Donor leucocyte infusion was given to six patients with i‐MC, but only one patient responded. Peripheral blood seems as valuable as bone marrow for chimaerism studies. In conclusion, serial quantitative chimaerism studies can identify patients with i‐MC who are at high risk for relapse of JMML. Immediate withdrawal of IST is advised in these patients.
The absence of CD56 on malignant plasma cells in the cerebrospinal fluid is the hallmark of multiple myeloma involving central nervous system
Authors: Chang Hong , Bartlett Eric S , Patterson Bruce , Chen Chris I , Yi Qi Long
Published: May 2005

By immunohistochemistry, the CD56‐positive myeloma cells were detected in three (38%) bone marrow (BM) and one (13%) cerebrospinal fluid (CSF) samples from eight patients with multiple myeloma involving the central nervous system (CNS MM). Of the three patients with CD56‐positive BM myeloma cells, two had CSF myeloma cells negative for CD56. In a control cohort of 84 MM patients without CNS involvement, the BM myeloma cells were CD56‐positive in 68 (80%) cases (P < 0·0001). The prevalence of CD56‐negative myeloma cells in the BM and CSF of our patients suggests that CD56 downregulation may play a role in the pathogenesis of CNS MM.
Host immune reactions and worm kinetics during the expulsion of Ascaris suum in pigs
Authors: Miquel N. , Roepstorff A. , Bailey M. , Eriksen L.
Published: May 2005

Pigs single inoculated with Ascaris suum eggs expel the majority of larvae between days 14 and 21 post inoculation (p.i.), but the role of the immune system in expulsion is unclear. To investigate the dynamics of immune responses before, during and after the expulsion of A. suum larvae, pigs inoculated with 10 000 A. suum eggs were sequentially necropsied. Ascaris suum gradually moved distally from days 10–14 p.i. and only a few larvae were left by day 21 p.i. Pronounced increases in mucosal A. suum‐specific IgA antibody secreting cells (ASCs) were already found by day 10 p.i. especially in the proximal jejunum, while only small increases in parasite‐specific IgM ASCs were observed by day 21 p.i. in both proximal and distal jejunum. No mucosal IgG ASC responses could be detected. Increases in systemic A. suum‐specific IgG1, IgM and to a lesser extent IgA antibodies were observed, while IgG2 remained almost unchanged. The levels of eosinophils and mast cells in the small intestinal mucosa did not change throughout infection. The results demonstrate that both systemic and mucosal A. suum‐specific effector mechanisms are strongly stimulated in A. suum single infections and indicate that mucosal IgA may be an important mediator in the expulsion of A. suum.
Immuno‐epidemiology ofAscaris lumbricoidesinfection in a high transmission community: antibody responses and their impact on current and future infection intensity
Authors: King E.‐M. , Kim H. T. , Dang N. T. , Michael E. , Drake L. , Needham C. , Haque R. , Bundy D. A. P. , Webster J. P.
Published: May 2005

The role of the humoral immune system in human infection withAscaris lumbricoidesremains unclear. This study documents an epidemiological investigation in a highly endemic community in Vietnam, whereby serum antibody levels were assessed before treatment and after a 6‐month reinfection period. These data were examined by correlation with infection status using an age‐structured approach in an attempt to help shed light on the role of the humoral immune response. The first part of this study characterized levels of all serum antibody isotypes from the community in response to antigens of both adult and larvalA. lumbricoides.Data were assessed in terms of their relation to host age and infection intensity with the aim to provide a broadly detailed account of immune responses to the parasite. In the second part, antibody responses to both life‐stages ofA. lumbricoidesin serum samples collected before anthelmintic chemotherapy were analysed in relation to intensity of re‐infection with the parasite 6 months following treatment. The results suggest that antibody responses may not confer protection from current infection or re‐infection withA. lumbricoidesand may not serve as reliable indicators of future infection intensity. Our results thereby lend support to the theory that immunity toA. lumbricoidesmay not be based on the humoral immune system.
Anaphylaxis during anesthesia: results of a 12‐year survey at a French pediatric center
Authors: Karila C. , Brunet‐Langot D. , Labbez F. , Jacqmarcq O. , Ponvert C. , Paupe J. , Scheinmann P. , de Blic J.
Published: May 2005

Background:  Following adverse reactions to anesthesia, tests are carried out to determine the mechanism of the reaction and to identify the agent responsible. No specific data are available in France concerning such skin tests in children.

Methods:  Between 1989 and 2001, we assessed hypersensitivity reactions to general anesthesia in 68 children. Thirty underwent more than one operation, for congenital malformations. Immunoglobulin (Ig)E‐mediated anaphylaxis was diagnosed on skin tests combined with the clinical history.

Results:  Grade I, II and III reactions were observed in 20, 27 and 21 children, respectively. IgE‐mediated anaphylaxis was diagnosed in 51 children: 31 (60.8%) for neuromuscular blocking agents (NMBA), 14 (27%) for latex, seven (14%) for colloids, five (9%) for opioids and six (12%) for hypnotics. Vecuronium was the NMBA causing the largest number of reactions. Cross reactivity to NMBA available in France was observed in 23 of 30 children (76%), particularly for vecuronium and atracurium or pancuronium.

The estimated frequency of IgE mediated anaphylactic reactions was one in 2100 operations. Based on our results, 25 children subsequently received a different anesthetic with no adverse reaction.

Conclusions:  As in adults, NMBA, then latex were responsible for most anaphylactic reactions during anesthesia. Our results confirm that skin tests with anesthetic agents are feasible and safe in children and improve the safety of subsequent anesthetic procedures.