bluuebunny/crossref_metadata_2025 huggingface dataset:
Pattern dynamics in a checkerboard map
Authors: Balmforth N. J. , Spiegel E. A.
Published: November 2004

Differential equations often have solutions in the forms of trains of coherent structures such as pulses and antipulses. For such sytems, the methods of singular perturbation theory permit the derivation of pattern maps that predict the sequence of spacings between successive pulses. Here we apply such a procedure to cases where two distinct kinds of pulse (or antipulse) may coexist in the system. In that case, direct application of the method leads to multivalued maps that make for complicated descriptions, especially when the succession of pulse types becomes chaotic. We show how this description may be simplified by using maps arrayed in checkerboard style to provide causal descriptions of both the successions of pulse spacings and the order in which the different kinds of pulse go by.
On the back-firing instability
Authors: Argentina M. , Rudzick O. , Velarde M. G.
Published: November 2004

The onset of the back-firing instability is studied in a one-dimensional spatially extended and dissipative system, where propagating localized solutions become unstable. It corresponds to the emission in the tail of a solitary wave of a new wave propagating in the opposite direction. The transition is illustrated, in geometrical terms, using a model normal form equation.
Theory of gaseous detonations
Authors: Clavin Paul
Published: November 2004

The objective of the present paper is to review some developments that have occurred in detonation theory over the last ten years. They concern nonlinear dynamics of detonation fronts, namely patterns of pulsating and/or cellular fronts, selection of the cell size, dynamical self-quenching, direct (blast) or spontaneous initiation, and transition from deflagration to detonation. These phenomena are all well documented by experiments since the sixties but remained unexplained until recently. In the first part of the paper, the patterns of cellular detonations are described by an asymptotic solution to nonlinear hyperbolic equations (reactive Euler equations) in the form of unsteady (sometime chaotic) and multidimensional traveling-waves. In the second part, turning points of quasi-steady solutions are shown to correspond to critical conditions of fully unsteady problems, either for (direct or spontaneous) initiation or for spontaneous failure (self-quenching). Physical insights are tentatively presented rather than technical aspects. The challenge is to identify the physical mechanisms with their relevant parameters, and more specifically to explain how the length-scales involved in detonation dynamics are larger by two order of magnitude (at least) than the length-scale involved in the steady planar traveling-wave solution (detonation thickness).
Degenerate principal series of quantum Harish–Chandra modules
Authors: Bershtein Olga
Published: November 2004

In this paper we study a quantum analog of a degenerate principal series of Uqsun,n-modules (0<q<1) related to the Shilov boundary of the quantum n×n-matrix unit ball. We give necessary and sufficient conditions for the modules to be simple and unitarizable and investigate their equivalence. These results are q-analogs of known classical results on reducibility and unitarizability of SU(n,n)-modules obtained by Johnson, Sahi, Zhang, Howe, and Tan.
Critical regimes and magnetohydrodynamic instabilities in a magneto-plasma-dynamic thruster
Authors: Zuin M. , Cavazzana R. , Martines E. , Serianni G. , Antoni V. , Bagatin M. , Andrenucci M. , Paganucci F. , Rossetti P.
Published: November 2004

An extensive experimental investigation of magnetic and electrostatic fluctuations in a magneto-plasma-dynamic (MPD) thruster, with and without the application of an external magnetic field, has shown that gross magnetohydrodynamic instabilities develop whenever the current rises beyond a threshold value. These instabilities are helical kink modes with azimuthal m and axial n periodicity m/n=1/1 and their occurrence can be described by the Kruskal–Shafranov stability criterion. The presence of these modes is found to be the cause of the loss of efficiency observed in MPD thrusters at high current.
Self-consistent theory of zonal flows in ion temperature gradient turbulence
Authors: Moestam Robert , Sheikh Dastgeer , Weiland Jan
Published: November 2004

A self-consistent theory of nonlinear zonal flows amidst complex background of ion temperature gradient (ITG) turbulence is presented. Starting with a reactive fluid model, a set of coupled nonlinear equations has been obtained in the form of Zakharov-like equations using the reductive perturbation method. These equations represent dynamical evolution of nonlinearly excited zonal flows and potential fluctuations of ITG turbulence. The derived equations have the potential to provide a qualitative explanation of the evolution of zonal flows and drift wave turbulence and their mutual interaction, which have been observed in recent gyrokinetic simulations [A. Dimits et al., Phys. Plasmas 7, 969 (2000)]. The nonlinear coupling coefficients are studied and show that the excitation of zonal flows is due to a resonance in the energy nonlinearity. The resonance turns out to be sensitive to fluid closure.
Frobenius monads and pseudomonoids
Authors: Street Ross
Published: November 2004

Six equivalent definitions of Frobenius algebra in a monoidal category are provided. In a monoidal bicategory, a pseudoalgebra is Frobenius if and only if it is star autonomous. Autonomous pseudoalgebras are also Frobenius. What it means for a morphism of a bicategory to be a projective equivalence is defined; this concept is related to “strongly separable” Frobenius algebras and “weak monoidal Morita equivalence.” Wreath products of Frobenius algebras are discussed.
Quasi-Hopf algebras and representations of octonions and other quasialgebras
Authors: Panaite Florin , Van Oystaeyen Freddy
Published: November 2004

Modules over a quasialgebra (here, by quasialgebra we mean a left H-module algebra, where H is a quasi-Hopf algebra), as defined by Albuquerque and Majid, coincide with modules over a certain associative algebra, a quasi-Hopf smash product. As a consequence of this, we get that the category of modules over the octonions is isomorphic to the category of modules over the algebra of 8×8 real matrices. We provide a new approach to the endomorphism quasialgebra associated to a left H-module, which in the finite dimensional case yields the same results as the one of Albuquerque and Majid. We discuss possible definitions as endomorphism quasialgebras for Heisenberg doubles of a finite dimensional quasi-Hopf algebra.
q
-conformal invariant equations and q-plane wave solutions
Authors: Dobrev V. K. , Petrov S. T.
Published: November 2004

We give new solutions of the quantum conformal deformations of the full Maxwell equations in terms of deformations of the plane wave. We study the compatibility of these solutions with the conservation of the current. We also start the study of quantum linear conformal (Weyl) gravity by writing the corresponding q-deformed equations.
Comment on “Kinetic effects on the parametric decays of circularly polarized electromagnetic waves in a relativistic pair plasma” [Phys. Plasmas 11, 3497 (2004)]
Authors: Stenflo L. , Shukla P. K.
Published: November 2004

It is argued that an improved version of the dispersion relation of Muñoz [Phys. Plasmas 11, 3497 (2004)] has already been obtained by Stenflo and Shukla [Phys. Plasmas 9, 4413 (2002)].
Laser electron acceleration by a plasma separator
Authors: Miyauchi K. , Miyazaki S. , Sakai K. , Kawata S. , Kong Q. , Andreev A. A. , Kikuchi T.
Published: November 2004

When electrons are accelerated by the ponderomotive force of an intense short-pulse laser, the electrons are accelerated at the head of the laser and they lose their energy gained at the tail of the laser. Therefore the electrons cannot finally obtain the laser energy. In this research, an overdense slab plasma separator is introduced in order to separate the accelerated electrons from the laser, just before they enter the deceleration phase. The laser is reflected by the plasma separator, so the electrons pass through the thin plasma separator without a significant influence and are successfully accelerated.
Beltrami-like fields created by baroclinic effect in two-fluid plasmas
Authors: Saleem H. , Yoshida Z.
Published: November 2004

A theory of two-dimensional plasma evolution with Beltrami-like flow and field due to baroclinic effect has been presented. Particular solution of the nonlinear two-fluid equations is obtained. This simple model can explain the generation of magnetic field without assuming the presence of a seed in the system. Coupled field and flow naturally grow together. The theory has been applied to estimate B-field in laser-induced plasmas and the result is in good agreement with experimental values.
Extremal covariant positive operator valued measures
Authors: Chiribella Giulio , D’Ariano Giacomo Mauro
Published: November 2004

We consider the convex set of positive operator valued measures (POVM) which are covariant under a finite dimensional unitary projective representation of a group. We derive a general characterization for the extremal points, and provide bounds for the ranks of the corresponding POVM densities, also relating extremality to uniqueness and stability of optimized measurements. Examples of applications are given.
Piezoelectric properties of lead-free CaBi4Ti4O15 thin films
Authors: Arai Fumihito , Motoo Kohei , Fukuda Toshio , Kato Kazumi
Published: November 2004

Ca Bi 4 Ti 4 O 15 (CBTi144) thin films are evaluated for use as lead-free thin-film piezoelectrics in microelectromechanical systems. CBTi144 thin films were prepared on Pt substrates by dip coating a precursor solution of metal alkoxides. We fabricated a piezoelectric bimorph actuator using those films and analyzed the displacement induced by the electric field. Young’s modulus was measured by the vibrating-reed technique and the piezoelectric constant d31 was derived by analysis of bending displacement and measurement of displacement-voltage curve. The measurements revealed that the CBTi144 films had a large piezoelectric constant d31 of 32pm∕V.
A Raman scattering-based method to probe the carrier drift velocity in semiconductors: Application to gallium nitride
Authors: Andrade-Neto A. V. , Vasconcellos A. R. , Luzzi R. , Freire V. N.
Published: November 2004

A single expression relating the carrier drift velocity in semiconductors under an electric field to Raman scattering data is derived resorting to a full nonequilibrium picture for electrons and holes. It allows one to probe with high optical precision both the ultrafast transient as well as the steady state carriers' drift velocity in semiconductor systems. This is achieved by simply modifying the experimental geometry, thus changing the angle between the transferred wave vector Q and the applied electric field E, and measuring the frequency shift promoted by the presence of the field to be observed in the single-particle and plasmon scattering spectra. An application to zinc-blende gallium nitride is presented to highlight the power of the method.
[001]-poled Pb(Zn1∕3Nb2∕3)O3-(6-7)%PbTiO3k31-actuators: Effects of initial domain structure, length orientation, and poling conditions
Authors: Rajan K. K. , Ng Y. S. , Zhang J. , Lim L. C.
Published: November 2004

Extremely high k31 and d31 values of 0.88 and −1850pC∕N were obtained from [001]-poled PZN-(6-7)%PT single-crystal plates but of different length orientations and initial domain structures. This composition also exhibits dielectric constant of 5500–6500 and a high depolarization temperature of ≈100°C.
A quantitative study of the relationship between the oxide charge trapping over the drain extension and the off-state drain leakage current
Authors: Huang Jiayi , Chen T. P. , Ang C. H. , Manju S. , Fung S.
Published: November 2004

In this letter, we report an approach to quantitative study of the relationship between the oxide charge trapping over the drain extension due to electrical stress and the off-state drain leakage current. It is found that positive charge trapping over the drain extension leads to a significant increase in the off-state drain current if the edge direct tunneling (EDT) is dominant in the drain current but in contrast, it leads to a reduction in the drain current if the band-to-band tunneling in the Si surface is dominant. A quantitative relationship between the charge trapping and the off-state drain leakage current in the EDT regime is established. From the measurement of the off-state current in the EDT regime, the charge trapping can be determined by using the approach developed in this study.
The effect of subgrid-scale models on the vortices computed from large-eddy simulations
Authors: da Silva Carlos B. , Pereira José C. F.
Published: November 2004

Direct numerical and large-eddy simulations (DNS/LES) of temporal plane jets are carried out in order to analyze the effect of the subgrid-scale (SGS) models on the vortices obtained from LES. The dynamics of the filtered vorticity norm (or filtered enstrophy) is analyzed through the application of a box filter to temporal DNS of turbulent plane jets (Reλ≈100), using a methodology similar to da Silva and Métais [J. Fluid Mech. 473, 103 (2002)]. Special emphasis is placed on the enstrophy SGS dissipation term, which represents the effect of the SGS models on the vortices computed from LES. When the filter is placed in the inertial range region the evolution of the vorticity norm is governed by the enstrophy production and enstrophy SGS dissipation, which represents, in the mean, a sink of resolved enstrophy. Thus the coherent vortices obtained from LES are subjected to an additional (nonviscous) dissipation mechanism. Locally, however, the enstrophy SGS dissipation can be either a sink or a source of resolved vorticity (forward/backward enstrophy cascade), but the forward cascade dominates, in analogy with what happens with the resolved kinetic energy equation. A priori tests are conducted using several SGS models in order to analyze their ability to represent the enstrophy SGS dissipation. The models analyzed are the Smagorinsky, structure function, filtered structure function, dynamic Smagorinsky, gradient, scale similarity, and mixed. It turns out that in terms of spatial localization all the models lead to a good correlation between the “real” and “modeled” enstrophy SGS dissipation. Moreover, all the SGS models, even of eddy-viscosity type, are able to provide enstrophy SGS backscatter. However, in terms of statistical behavior the eddy-viscosity models do not provide enough enstrophy backscatter as the non-eddy-viscosity models. LES are carried out and show that the Smagorinsky, structure function, and mixed models cause excessive vorticity dissipation compared to the other models, and although the enstrophy SGS dissipation affects mainly the smallest resolved scales, it may affect also some low-wave numbers. An estimation of the “vorticity error” and its wave number dependence is given, for each SGS model. Both a priori tests and LES show that the dynamic Smagorinsky and filtered structure function models seem to be the best suited to a correct prediction of the resolved vorticity field.
High-power and reliable operation of vertical light-emitting diodes on bulk GaN
Authors: Cao X. A. , Arthur S. D.
Published: November 2004

In Ga N ∕ Ga N light-emitting diodes (LEDs) with lateral and vertical geometries have been fabricated on free-standing GaN substrates. Current spreading was significantly enhanced in the vertical LED, leading to a reduced series resistance of 7Ω compared to 12.2 and 14.2Ω for the lateral LEDs on GaN and sapphire, respectively. As a result, the light output and power conversion efficiency of the vertical LED on GaN were greatly improved at high injection currents. The vertical LED was subjected to a stress test at 400mA and showed minimal degradation of optical power, whereas the same stress resulted in the destruction of the lateral LED on sapphire due to increased current crowding and self-heating. However, lateral LEDs on sapphire with optimized current spreading exhibited excellent reliability, indicating the presence of a high density of dislocations (∼109cm−2) in the heteroepitaxial device does not accelerate LED degradation at current densities up to 700A∕cm2.
On the thermal field in the impulsive Rayleigh flow
Authors: Pozzi Amilcare , Tognaccini Renato
Published: November 2004

This paper reconsiders the celebrated analysis of the thermal field arising when an infinite plate is impulsively accelerated to a constant speed in a fluid (Rayleigh flow). The analysis has been completed by proposing an analytical solution valid for any Prandtl number in both the cases of isothermal or adiabatic wall, also including the effect of dissipation of kinetic energy. Very simple exact analytical expressions of the recovery factor and of the Nusselt number have been obtained. The results have been extended to compressible flow by the Stewartson–Dorodnitsin transformation.
Observation of fast spontaneous emission decay in GaInAsP photonic crystal point defect nanocavity at room temperature
Authors: Baba Toshihiko , Sano Daisuke , Nozaki Kengo , Inoshita Kyoji , Kuroki Yusuke , Koyama Fumio
Published: November 2004

The spontaneous emission decay in a photonic crystal slab nanocavity with a GaInAsP quantum well active region was measured at room temperature. Even far below lasing threshold, the decay was much faster than that for the as-grown wafer. A consideration including the enhanced spontaneous emission rate by the Purcell effect, intraband relaxation of carriers, nonradiative surface recombination, spatial hole burning, and carrier diffusion enabled us to explain different decay lifetime between on- and off-resonant conditions and between different size cavities. As a result, >16-fold shorter spontaneous emission lifetime was estimated, which strongly suggests the existence of a large Purcell effect.
In situ real time process characterization in nanoimprint lithography using time-resolved diffractive scatterometry
Authors: Yu Zhaoning , Gao He , Chou Stephen Y.
Published: November 2004

To optimize nanoimprint lithography (NIL), it is essential to be able to characterize and control the NIL process in situ and in real time. Here, we present a method for in situ real-time NIL process characterization using time-resolved diffractive scatterometry (TRDS). A surface relief diffraction grating is used as the imprint mold, and the diffracted light intensity is monitored continuously during the imprint process. We use a scalar diffraction model to calculate the diffraction intensity as a function of the mold penetration ratio. Simulations show good agreement with the experimental results. Our results indicate that TRDS offers a powerful characterization tool that can be used for in situ, real-time NIL process control.
AlGaN
∕
GaN
metal-oxide-semiconductor heterostructure field-effect transistor with oxidized Ni as a gate insulator
Authors: Oh C. S. , Youn C. J. , Yang G. M. , Lim K. Y. , Yang J. W.
Published: November 2004

We fabricated the AlGaN∕GaN metal-oxide-semiconductor heterostructure field-effect transistor (MOSHFET) using the oxidized Ni(NiO) as a gate oxide and compared electrical properties of this device with those of a conventional AlGaN∕GaN heterostructure field-effect transistor (HFET). NiO was prepared by oxidation of Ni metal of 100Å at 600°C for 5min in air ambient. For HFET and MOSHFET with a gate length of 1.2μm, the maximum drain currents were about 800mA∕mm and the maximum transconductances were 136 and 105mS∕mm, respectively. As the oxidation temperature of Ni increased from 300 to 600°C the gate leakage current decreased dramatically due to the formation of insulating NiO. The gate leakage current for the MOSHFET with the oxidized NiO at 600°C was about four orders of magnitude smaller than that of the HFET. Based on the dc characteristics, NiO as a gate oxide is comparable with other gate oxides.
Measurement of interface potential change and space charge region across metal/organic/metal structures using Kelvin probe force microscopy
Authors: Tal O. , Gao W. , Chan C. K. , Kahn A. , Rosenwaks Y.
Published: November 2004

We report on high-resolution potential measurements across complete metal/organic molecular semiconductor/metal structures using Kelvin probe force microscopy in inert atmosphere. It is found that the potential distribution at the metal/organic interfaces is in agreement with an interfacial abrupt potential changes and the work function of the different metals. The potential distribution across the organic layer strongly depends on its purification. In pure Alq3 the potential profile is flat, while in nonpurified layers there is substantial potential bending probably due to the presence of deep traps. The effect of the measuring tip is calculated and discussed.
Nonlinear transport imaging by scanning impedance microscopy
Authors: Shin J. , Meunier V. , Baddorf A. P. , Kalinin S. V.
Published: November 2004

Scanning probe microscopy is an established tool for characterization of the linear static and frequency-dependent lateral electronic transport in materials and devices at the nanoscale. In this letter, a modified scanning impedance microscopy (SIM) technique is proposed to extend the nanoscale transport measurements of intrinsic material properties to the nonlinear regime, through detection of frequency harmonics, and exemplified by a detailed study of a prototypical metal–semiconductor interface. The imaging mechanism, surface–tip contrast transfer, optimal experimental conditions, and potential applications of nonlinear SIM are discussed. This technique can be readily transferred to most cantilever-based scanning probe microscopes.
Electric-field driven jetting from dielectric liquids
Authors: Jayasinghe S. N. , Edirisinghe M. J.
Published: November 2004

Three dielectric (electrical conductivity ∼10−13Sm−1) Newtonian liquids with viscosity in the range 1–100 mPa s were passed through a needle at a controlled flow rate under the influence of an electric field. At an electric field strength of 1.5kV∕mm, the liquid exiting the needle instantaneously transformed from dripping droplets to an elliptically pendent droplet from the apex of which a fine jet evolved. Thus, a jet can be obtained on demand, and in this letter we define this phenomenon and explain a basis for it.
Abnormal temperature dependence of dielectric constant in (Ba0.7Sr0.3)TiO3 thin films
Authors: Yang Hao , Miao Jun , Chen Bin , Zhao Li , Xu Bo , Dong Xiaoli , Cao Lixin , Qiu Xianggang , Zhao Bairu
Published: November 2004

Pt ∕ ( Ba 0.7 Sr 0.3 ) TiO 3 ∕ YBa 2 Cu 3 O 7 − x capacitors were fabricated on LaAlO3 substrates. Dielectric and ferroelectric properties were measured in the temperature range from 20 to 250K. It was found that the dielectric constant decreased with decreasing temperature from 250 to ∼150K but then increased as the temperature continued to decrease to 20K. Considering this phenomenon along with the irregular temperature dependence of spontaneous polarization, it is indicated that such abnormal behavior originates in a second-order structural phase transition in the (Ba1−xSrx)TiO3 thin film in the vicinity of 150K.
Controlling Er–Tm interaction in Er and Tm codoped silicon-rich silicon oxide using nanometer-scale spatial separation for efficient, broadband infrared luminescence
Authors: Seo Se-Young , Shin Jung H.
Published: November 2004

The effect of nanometer-scale spatial separation between Er3+ and Tm3+ ions in Er and Tm codoped silicon-rich silicon oxide (SRSO) films is investigated. Er and Tm codoped SRSO films, which consist of nanocluster Si(nc-Si) embedded inside SiO2 matrix, were fabricated with electron cyclotron resonance-plasma enhanced chemical vapor deposition of SiH4 and O2 with concurrent sputtering of Er and Tm metal targets. Spatial separation between Er3+ and Tm3+ ions was achieved by depositing alternating layers of Er- and Tm-doped layers of varying thickness while keeping the total film thickness the same. The films display broadband infrared photoluminescence (PL) from 1.5 to 2.0μm under a single source excitation due to simultaneous excitation of Er3+ and Tm3+ ions by nc-Si. Increasing the layer thickness from 0 to 72nm increases the Er3+ PL intensity nearly 50-fold while the Tm3+ PL intensity is unaffected. The data are well-explained by a model assuming a dipole–dipole interaction between excited Er3+ and Tm3+ ions, and suggest that by nanoscale engineering, efficient, ultrabroadband infrared luminescence can be obtained in an optically homogeneous material using a single light source.
Epitaxially induced high temperature (>900K) cubic-tetragonal structural phase transition in BaTiO3 thin films
Authors: Bai Feiming , Zheng Haimei , Cao Hu , Cross L. E. , Ramesh R. , Li Jiefang , Viehland D.
Published: November 2004

For (001)c oriented BaTiO3 thin films, it has been found that epitaxial constraint can result in a dramatic increase in the temperature of a tetragonal (T) structural phase transition. For 2000-Å-thick films grown directly on SrTiO3 substrates, a T→cubic (C) phase transition was found on heating at >950K, where the lattice constant changed smoothly with temperature. It was also found for films of the same thickness that the T→C transition is nearly restored to that of bulk crystals by the use of a buffer layer, which relaxes the epitaxial constraint. These results provide evidence of an epitaxially induced high temperature structural phase transition in BaTiO3 thin films, where the ferroelectric (internal) and structural (external) aspects of the phase transition are decoupled.
Electronic structure and bonding properties of Si-doped hydrogenated amorphous carbon films
Authors: Ray S. C. , Bao C. W. , Tsai H. M. , Chiou J. W. , Jan J. C. , Kumar K. P. Krishna , Pong W. F. , Tsai M.-H. , Wang W.-J. , Hsu C.-J. , Okpalugo T. I. T. , Papakonstantinou P. , McLaughlin J. A.
Published: November 2004

This work investigates the C K-edge x-ray absorption near-edge structure (XANES), valence-band photoelectron spectroscopy (PES), and Fourier transform infrared (FTIR) spectra of Si-doped hydrogenated amorphous carbon films. The C K-edge XANES and valence-band PES spectra indicate that the sp2∕sp3 population ratio decreases as the amount of tetramethylsilane vapor precursor increases during deposition, which suggest that Si doping% enhances sp3 and reduces sp2-bonding configurations. FTIR spectra show the formation of a polymeric sp3 C–Hn structure and Si–Hn bonds, which causes the Young’s modulus and hardness of the films to decrease with the increase of the Si content.
Microfluidic manipulation via Marangoni forces
Authors: Farahi R. H. , Passian A. , Ferrell T. L. , Thundat T.
Published: November 2004

A convective flow system is engendered when two liquid droplets, or a liquid droplet and a solid surface, are maintained at different temperatures. Such flows give rise to Marangoni forces which under proper conditions prevent droplet coalescence, cause fluid motion, and dewetting. We present a study of adsorbed and applied fluid movement on a solid surface driven by surface tension gradients created by thermal gradients. Flexible control over the silicone oil and 1,3,5-trinitrotoluene movement is accomplished with an array of individually controllable gold thin film thermal elements on a fused silica substrate surface. We thus demonstrate unlimited fluid movements in one dimension.
Two-beam interferometric encoding of photoluminescent gratings in LiF crystals by high-brightness tabletop soft x-ray laser
Authors: Tomassetti G. , Ritucci A. , Reale A. , Arrizza L. , Flora F. , Montereali R. M. , Faenov A. , Pikuz T.
Published: November 2004

Two-beam interferometric encoding of periodic lines of permanent color centers in LiF has been obtained by use of an intense and high spatially coherent soft x-ray laser beam. A spatial resolution of the lines less than 1μm is demonstrated. We have used the 46.9nm laser pulses (0.3mJ, 1.7ns at 0.2Hz) produced in compact capillary discharges. Due to the low penetration depth of their radiation, their high brightness and spatial coherence, soft x-ray lasers can represent a powerful tool to encode integrated optical devices having low dimensionality and high spatial resolution inside optically transparent dielectrics, in extremely short exposure times.
Effect of thermal strain on the ferroelectric phase transition in polycrystalline Ba0.5Sr0.5TiO3 thin films studied by Raman spectroscopy
Authors: Tenne D. A. , Soukiassian A. , Xi X. X. , Taylor T. R. , Hansen P. J. , Speck J. S. , York R. A.
Published: November 2004

We have applied Raman spectroscopy to study the influence of thermal strain on the vibrational properties of polycrystalline Ba0.5Sr0.5TiO3 films. The films were grown by rf magnetron sputtering on Pt∕SiO2 surface using different host substrates: strontium titanate, sapphire, silicon, and vycor glass. These substrates provide a systematic change in the thermal strain while maintaining the same film microstructure. From the temperature dependence of the ferroelectric A1 soft phonon intensity, the ferroelectric phase transition temperature, TC, was determined. We found that TC decreases with increasing tensile stress in the films. This dependence is different from the theoretical predictions for epitaxial ferroelectric films. The reduction of the ferroelectric transition temperature with increasing biaxial tensile strain is attributed to the suppression of in-plane polarization due to the small lateral grain size in the films.
Double resonance optical pumping spectrum and its application for frequency stabilization of a laser diode
Authors: Moon H. S. , Lee W. K. , Lee L. , Kim J. B.
Published: November 2004

We present double resonance optical pumping (DROP) spectra for the 5P3∕2–4D3∕2 transition and the 5P3∕2–4D5∕2 transition of R87b and we use these spectra for frequency stabilization in the 1.5μm region. The spectra, compared to the conventional double resonance spectrum, show a good signal-to-noise ratio and a narrow spectral linewidth for laser frequency stabilization. The different intensities of the hyperfine states were attributed to the different rates of double resonance optical pumping into the other ground state. When we stabilized the frequency of a 1.5μm laser diode to the DROP spectrum, the best frequency stability was 1×10−11 after 100s.
Phase transitional behavior and piezoelectric properties of (Na0.5K0.5)NbO3–LiNbO3 ceramics
Authors: Guo Yiping , Kakimoto Ken-ichi , Ohsato Hitoshi
Published: November 2004

Lead-free piezoelectric ceramics (1−x)(Na0.5K0.5)NbO3–xLiNbO3 {[Lix(Na0.5K0.5)1−x]NbO3} (x=0.04–0.20) have been synthesized by an ordinary sintering technique. The materials with perovskite structure is orthorhombic phase at x⩽0.05 and becomes tetragonal phase at x⩾0.07, a phase K3Li2Nb5O15 with tetragonal tungsten bronze structure begins to appear at x=0.08 and becomes dominant with increasing the content of LiNbO3. A morphotropic phase boundary between orthorhombic and tetragonal phases is found in the composition range 0.05<x<0.07. Analogous to Pb(Zr,Ti)O3, the piezoelectric and electromechanical properties are enhanced for compositions near the morphotropic phase boundary. Piezoelectric constant d33 values reach 200–235pC∕N. Electromechanical coefficients of the planar mode and the thickness mode reach 38%–44% and 44%–48%, respectively. The Curie temperatures (TC) of [Lix(Na0.5K0.5)1−x]NbO3 (x=0.04–0.20) are in the range of 452–510°C, at least 100°C higher than that of conventional Pb(Zr,Ti)O3. Our results show that [Lix(Na0.5K0.5)1−x]NbO3 is a good lead-free high-temperature piezoelectric ceramic.
Study of the interaction of 4H–SiC and 6H–SiC(0001)Si surfaces with atomic nitrogen
Authors: Losurdo Maria , Giangregorio Maria M. , Bruno Giovanni , Brown April , Kim Tong-Ho
Published: November 2004

The interaction of atomic nitrogen with 4H– and 6H–SiC(0001) Si-face surfaces is investigated. Clean and atomically smooth terraced surfaces obtained by in situ cleaning using atomic hydrogen have been exposed at 200°C and 750°C to atomic nitrogen produced by a rf remote N2 plasma. Spectroscopic ellipsometry is used for real-time monitoring of the kinetics of SiC surface modifications, and determining the thickness and properties of the nitrided layer. Surface potential measurements reveal the band bending of the nitrided SiC surface. An improvement in the heteroepitaxy of GaN on the low-temperature nitrided SiC surface is found.
Critical point energy as a function of electric field determined by electroreflectance of surface-intrinsic-n+ type doped GaAs
Authors: Chen Y. S. , Wu K. S. , Wang D. P. , Huang K. F. , Huang T. C.
Published: November 2004

Electroreflectance of surface-intrinsic-n+ type doped GaAs has been measured over a various biased voltage. The spectra have exhibited many Franz–Keldysh oscillations (FKOs) above band gap energy Eg. The electric field F and critical point energy Ec can be determined from the slope and intercept of FKOs fitting. Hence, we can obtain Ec as a function of F. In most of previous works, Ec is taken as Eg. However, it was found that Ec increases with F in this work. In order to explain this, the gain of energy of electron and hole in F was discussed.
Thermal stability of electron traps in GaN grown by metalorganic chemical vapor deposition
Authors: Johnstone D. , Doğan S. , Leach J. , Moon Y. T. , Fu Y. , Hu Y. , Morkoç H.
Published: November 2004

Deep level transient spectroscopy was used to investigate the thermal stability of electron traps in n-type GaN grown by metalorganic chemical vapor deposition. The concentration of traps at 160 and at 500K increased more than fivefold over the course of several 700K anneal cycles, while a peak at 320K increased by a factor of only 1.19. The increase in the trap concentration with repeated annealing might be due to a mobile trap or loss of passivant. Hydrogen is very likely present in high concentration in the epilayer, and its passivating effects may be lost with annealing.
Effect of anharmonicity of the strain energy on band offsets in semiconductor nanostructures
Authors: Lazarenkova Olga L. , von Allmen Paul , Oyafuso Fabiano , Lee Seungwon , Klimeck Gerhard
Published: November 2004

Anharmonicity of the interatomic potential is taken into account for the quantitative simulation of the conduction and valence band offsets for strained semiconductor heterostructures. The anharmonicity leads to a weaker compressive hydrostatic strain than that obtained with the commonly used quasiharmonic approximation of the Keating model. Compared to experiment, inclusion of the anharmonicity in the simulation of strained InAs∕GaAs nanostructures results in an improvement of the electron band offset computed on an atomistic level by up to 100meV.
Enhancement of rare-earth–transition-metal exchange interaction in Pr2Fe17 probed by inelastic neutron scattering
Authors: Magnani N. , Carretta S. , Amoretti G. , Pareti L. , Paoluzi A. , Caciuffo R. , Stride J. A.
Published: November 2004

The fundamental magnetic interactions of Pr2Fe17 are studied by inelastic neutron scattering and anisotropy field measurements. Data analysis confirms the presence of three magnetically inequivalent sites, and reveals an exceptionally large value of the exchange field. The unexpected importance of J-mixing effects in the description of the ground-state properties of Pr2Fe17 is shown, and possible applications of related compounds are envisaged.
Optical levitation in a Bessel light beam
Authors: Garcés-Chávez V. , Roskey D. , Summers M. D. , Melville H. , McGloin D. , Wright E. M. , Dholakia K.
Published: November 2004

A vertically oriented zero order Bessel light beam is shown to create a one-dimensional array of trapped particles over extended (millimeter) distances. The particles take up equilibrium positions over the entire length of the beam and this is a consequence of the interplay between optical scattering and the self-healing properties of the Bessel beam. This work has analogies to recent studies of optically bound matter and allows for the simple creation of one-dimensional particle chains and their subsequent spectroscopic analysis.
Scattering loss in silicon-on-insulator rib waveguides fabricated by inductively coupled plasma reactive ion etching
Authors: Wang Yongjin , Lin Zhilang , Cheng Xinli , Zhang Changsheng , Gao Fan , Zhang Feng
Published: November 2004

Inductively coupled plasma reactive ion etching (ICPRIE) was used to etch rib the waveguide and U groove to achieve the integration of self-alignment connection between single mode fiber and rib waveguide in silicon-on-insulator (SOI) wafer. Interface roughness is one of the consequences of an ICPRIE process. Endface roughness, surface roughness, and sidewall roughness result in increasing scattering losses for waveguides. A series of atomic force microscope measurements were carried out to demonstrate the root-mean-square (rms) roughness of SOI rib waveguide etched by ICPRIE method. According to scalar scattering theory and Tien’s theory, scattering loss induced by the rms roughness was studied systematically.
Magnetic and morphological characteristics of nickel nanoparticles films produced by femtosecond laser ablation
Authors: Ausanio G. , Barone A. C. , Iannotti V. , Lanotte L. , Amoruso S. , Bruzzese R. , Vitiello M.
Published: November 2004

We have used the technique of femtosecond (fs) laser ablation in a vacuum to produce films of nickel nanoparticles. A peculiarity of this fs laser deposition is the significant shape and orientation anisotropy of the nanoparticles, which are oblate ellipsoids with the major axis parallel to the deposition substrate. The deposited films present unique magnetic properties, and, in specific conditions, very high remanence ratios (up to 0.7) accompanied with relatively low values of saturation and coercive fields can be obtained. We have interpreted these results in terms of the mentioned anisotropies, and of the occurrence of a thermally induced in-plane tensile stress, which is a function of the nanoparticles size.
Power broadening of the exciton linewidth in a single InGaAs∕GaAs quantum dot
Authors: Stufler Stefan , Ester Patrick , Zrenner Artur , Bichler Max
Published: November 2004

We use high-resolution photocurrent spectroscopy to investigate the ground state of a single quantum dot. In the limit of low optical excitation power, we observe a ground state linewidth down to 4μeV. With increasing excitation intensities, the linewidth shows a characteristic power broadening. This effect is a direct consequence of the saturation of the absorption in a two-level system under conditions of high excitation intensities. From a comparison of both effects, we conclude that power-dependent dephasing is negligible in our system.
Trading off Species Protection and Timber Production in Forests Managed for Multiple Objectives
Authors: Marianov Vladimir , Snyder Stephanie , ReVelle Charles
Published: November 2004

We address a multiobjective forest-management problem that maximizes harvested timber volume and maximizes the protection of species through the selection of protected habitat reserves. As opposed to reserving parcels of the forest for general habitat purposes, as most published works do, the model we present, and its several variants, concentrate on the preservation status of each one of the species living in the forest under study. Thus, all of the formulations we propose trade off harvested timber volume against the weighted number of preserved species. Each formulation represents a different management policy. Casting the models in a static setting allows us to analyze the effect of several management policies through computational experience with different forest-stucture — species relationships.
A clock gene,
period
, plays a key role in long-term memory formation in
Drosophila
Authors: Sakai Takaomi , Tamura Takuya , Kitamoto Toshihiro , Kidokoro Yoshiaki
Published: November 2004

The cAMP-responsive transcription factor, CREB, is required for formation of long-term memory (LTM) in
Drosophila melanogaster
and regulates transcription of a circadian clock gene,
period
(
per
). Involvement of CREB both in LTM and circadian rhythm raises the possibility that
per
also plays a role in LTM. Assaying the experience-dependent courtship inhibition in male flies as a measure for LTM, we show here that
per
mutants are defective in LTM formation. This defect was rescued by induction of a wild-type
per
transgene in a
per
-null mutant, and overexpression of
per
enhanced LTM formation in the wild-type background. Furthermore, we found that synaptic transmission through
per
-expressing cells is most likely to be required during retrieval of LTM. In contrast, mutations in other clock genes (
timeless
,
dClock
, and
cycle
) did not affect LTM formation. Thus, independent of the core oscillator of circadian clock,
per
plays a key role in LTM formation.
Transition state and encounter complex for fast association of cytochrome
c
2
with bacterial reaction center
Authors: Miyashita Osamu , Onuchic José N. , Okamura Melvin Y.
Published: November 2004

Electrostatic interactions strongly enhance the electron transfer reaction between cytochrome (Cyt)
c
2
and reaction center (RC) from photosynthetic bacteria, yielding a second-order rate constant,
k
2
≈ 10
9
s
-1
·M
-1
, close to the diffusion limit. The proposed mechanism involves an encounter complex (EC) stabilized by electrostatic interactions, followed by a transition state (TS), leading to the bound complex active in electron transfer. The effect of electrostatic interactions was previously studied by Tetreault
et al.
[Tetreault, M., Cusanovich, M., Meyer, T., Axelrod, H. & Okamura, M. Y. (2002)
Biochemistry
41, 5807-5815] by measuring
k
2
for RC and Cyt molecules with modified charged residues at the binding interface. The present work is a computational analysis of this kinetic study to determine the ensemble of configurations of the TS and EC. Changes in the TS energies due to different mutations were compared with differences in the calculated electrostatic energies for a wide range of Cyt/RC configurations. The TS ensemble, obtained from structures having the highest correlation coefficients in the comparison with experimental data, has the Cyt displaced by ≈10 Å from its position in x-ray crystal structure, close to the average position of the EC ensemble, with strong electrostatic interactions between Cyt on the M subunit side of the RC surface. The heme of the Cyt is oriented toward Tyr L162 on the RC, the tunneling contact in the bound final state on the RC. The similarity between the structures of the EC, TS, and bound state can account for the rapid rate of association responsible for fast diffusion-controlled electron transfer.
Inorganic polyphosphate in the origin and survival of species
Authors: Brown Michael R. W. , Kornberg Arthur
Published: November 2004

Inorganic polyphosphate (poly P), in chains of tens to hundreds of phosphate residues, linked by high-energy bonds, is environmentally ubiquitous and abundant. In prebiotic evolution it could have provided a flexible, polyanionic scaffold to assemble macromolecules. It has been conserved in every cell in nature. In prokaryotes, a major poly P synthetic enzyme is poly P kinase 1 (PPK1), which is found in 100 bacterial genomes, including numerous pathogens. Null mutants of PPK1, with low poly P levels, are defective in survival: namely, they show defective responses to physical/chemical stresses and predation. Pathogens with a PPK1 deletion are defective in biofilm formation, quorum sensing, general stress and stringent responses, motility, and other virulence properties. With the exception of
Dictyostelium
, PPK1 is absent in eukaryotes and provides a novel target for chemotherapy that would affect both virulence and susceptibility to antibacterial compounds. Remarkably, another PPK in
Dictyostelium discoideum
(PPK2) is an actin-related protein (Arp) complex that is polymerized into an actin-like filament, concurrent with its reversible synthesis of a poly P chain from ATP.
Age-related reduction in microcolumnar structure in area 46 of the rhesus monkey correlates with behavioral decline
Authors: Cruz Luis , Roe Daniel L. , Urbanc Brigita , Cabral Howard , Stanley H. E. , Rosene Douglas L.
Published: November 2004

Many age-related declines in cognitive function are attributed to the prefrontal cortex, area 46 being especially critical. Yet in normal aging, studies indicate that neurons are not lost in area 46, suggesting that impairments result from more subtle processes. One cortical feature that is functionally important, but that has not been examined in normal aging because of a lack of efficient quantitative methods, is the vertical arrangement of neurons into microcolumns, a fundamental computational unit of the cortex. By using a density-map method derived from condensed-matter physics, we quantified microcolumns in area 46 of seven young and seven aged rhesus monkeys that had been cognitively tested. This analysis demonstrated that there is no age-related reduction in total neuronal density or in microcolumn width, length, or periodicity. There was, however, a statistically significant decrease in the strength of microcolumns, indicating microcolumnar disorganization. This reduction in strength was significantly correlated with age-related cognitive decline on tests of spatial working memory and recognition memory independent of the effect of age. Modeling demonstrated that random neuron displacements of ≈30% of a neuronal diameter (<3 μm) produced the observed reduction in strength. Hence, it is possible that, with changes in dendrites and myelinated axons, subtle displacements of neurons occur that alter microcolumnar structure and correlate with age-induced dysfunction. Therefore, quantitative measurement of microcolumnar structure may provide a sensitive morphological method to assay microcolumnar function in aging and other conditions.
A polymer library approach to suicide gene therapy for cancer
Authors: Anderson Daniel G. , Peng Weidan , Akinc Akin , Hossain Naushad , Kohn Anat , Padera Robert , Langer Robert , Sawicki Janet A.
Published: November 2004

Optimal gene therapy for cancer must (
i
) deliver DNA to tumor cells with high efficiency, (
ii
) induce minimal toxicity, and (
iii
) avoid gene expression in healthy tissues. To this end, we generated a library of >500 degradable, poly(β-amino esters) for potential use as nonviral DNA vectors. Using high-throughput methods, we screened this library
in vitro
for transfection efficiency and cytotoxicity. We tested the best performing polymer, C32, in mice for toxicity and DNA delivery after intratumor and i.m. injection. C32 delivered DNA intratumorally ≈4-fold better than one of the best commercially available reagents, jetPEI (polyethyleneimine), and 26-fold better than naked DNA. Conversely, the highest transfection levels after i.m. administration were achieved with naked DNA, followed by polyethyleneimine; transfection was rarely observed with C32. Additionally, polyethyleneimine induced significant local toxicity after i.m. injection, whereas C32 demonstrated no toxicity. Finally, we used C32 to deliver a DNA construct encoding the A chain of diphtheria toxin (DT-A) to xenografts derived from LNCaP human prostate cancer cells. This construct regulates toxin expression both at the transcriptional level by the use of a chimeric-modified enhancer/promoter sequence of the human prostate-specific antigen gene and by DNA recombination mediated by Flp recombinase. C32 delivery of the A chain of diphtheria toxin DNA to LNCaP xenografts suppressed tumor growth and even caused 40% of tumors to regress in size. Because C32 transfects tumors locally at high levels, transfects healthy muscle poorly, and displays no toxicity, it may provide a vehicle for the local treatment of cancer.