bluuebunny/crossref_metadata_2025 huggingface dataset:
A hierarchy of nonlinear evolution equations and finite-dimensional involutive systems
Authors: Qiao Zhijun
Published: July 2002

A spectral problem and an associated hierarchy of nonlinear evolution equations are presented in this article. In particular, the reductions of the two representative equations in this hierarchy are given: one is the nonlinear evolution equation rt=−αrx−2iαβ‖r2‖r which looks like the nonlinear Schrödinger equation, the other is the generalized derivative nonlinear Schrödinger equation rt= 1/2iαrxx−iα‖r‖2r−αβ(‖r‖2r)x −αβ‖r‖2rx−2iαβ2‖r‖4r which is just a combination of the nonlinear Schrödinger equation and two different derivative nonlinear Schrödinger equations [D. J. Kaup and A. C. Newell, J. Math. Phys. 19, 789 (1978); M. J. Ablowitz, A. Ramani, and H. Segur, J. Math. Phys. 21, 1006 (1980)]. The spectral problem is nonlinearized as a finite-dimensional completely integrable Hamiltonian system under a constraint between the potentials and the spectral functions. At the end of this article, the involutive solutions of the hierarchy of nonlinear evolution equations are obtained. Particularly, the involutive solutions of the reductions of the two representative equations are developed.
Zero modes of rotationally symmetric generalized vortices and vortex scattering
Authors: Burzlaff J. , Tchrakian D. H.
Published: July 2002

Zero modes of rotationally symmetric vortices in a hierarchy of generalized Abelian Higgs models are studied. Under the finite energy and the smoothness condition, it is shown, that in all models, n self-dual vortices superimposed at the origin have 2n modes. The relevance of these modes for vortex scattering is discussed: first, in the context of the slow-motion approximation; second, a corresponding Cauchy problem for an all head-on collision of n vortices is formulated. It is shown that the solution of this Cauchy problem has a π/n symmetry.
Nonlocal symmetries and nonlocal conservation laws of Maxwell’s equations
Authors: Anco Stephen C. , Bluman George
Published: July 2002

Nonlocal symmetries are obtained for Maxwell’s equations in three space–time dimensions through the use of two potential systems involving scalar and vector potentials for the electromagnetic field. Corresponding nonlocal conservation laws are derived from these symmetries. The conservation laws yield nine functionally independent constants of motion which cannot be expressed in terms of the constants of motion arising from local conservation laws for space–time symmetries. These nine constants of motion represent additional conserved quantities for the electromagnetic field in three space–time dimensions.
On the space-time characteristics of wall-pressure fluctuations
Authors: Choi Haecheon , Moin Parviz
Published: July 2002

A database obtained by direct numerical simulation of turbulent channel flow was used to compute the three-dimensional frequency/wave-number spectrum of wall-pressure fluctuations. The spectrum was used to deduce scaling laws for pressure fluctuations and to evaluate the similarity form for the power spectrum. The convection velocity as a function of frequency, wave number, and spatial and temporal separations was calculated and compared with the experimental data. The problem of artificial ‘‘acoustics’’ in numerical simulation of incompressible flows is discussed.
Is intermittent motion of outer flow in the turbulent boundary layer deterministic chaos?
Authors: Tsuji Yoshiyuki , Honda Katsuya , Nakamura Ikuo , Sato Shinichi
Published: July 2002

Intermittent phenomena observed in the outer regions of the turbulent boundary layer are studied. A new idea is proposed in which the dynamics generating the intermittent phenomena can be described by a one-dimensional map; Xi+1=(1+ε)Xi+uXzi, for 0≤Xi≤Xc<1 (mode 1, z>1, u>0). The binary sequence {si} is constructed from carefully processed data of instantaneous streamwise velocities, and also from the map. The encoding is made in such a way that the turbulent state is referred to as si=1 and the nonturbulent state as si=0 at a discretized time i. Both sequences are found to have the common essential properties of intermittent chaos; the probability P(l) of finding nonturbulent states with length l exhibits the power law with an exponent r for l<lc, lc being a cutoff. From the exponent r, one can assign z almost equal to 4, while the control parameter ε is closely related to the distance from the wall. The scaling function of P(l) agrees very well with the one predicted from the map. The cutoff length lc is found to be associated with the average period of bursting.
Reynolds number effects in Lagrangian stochastic models of turbulent dispersion
Authors: Sawford B. L.
Published: July 2002

A second-order autoregressive equation is used to model the acceleration of fluid particles in turbulence in order to study the effect of Reynolds number on Lagrangian turbulence statistics. It is shown that this approach provides a good representation of dissipation subrange structure of Lagrangian velocity and acceleration statistics. The parameters of the model, two time scales representing the energy-containing and dissipation scales, are determined by matching the model velocity autocorrelation function to Kolmogorov similarity forms in the inertial subrange and the dissipation subrange. The model is tested against the Lagrangian statistics obtained by Yeung and Pope [J. Fluid Mech. 207, 531 (1989)] from direct numerical simulations of turbulence. Agreement between the model predictions and simulation data for second-order Lagrangian statistics such as the velocity structure function, the acceleration correlation function, and the dispersion of fluid particles is excellent, indicating that the main departures from Kolmogorov’s theory of local isotropy shown by the simulation data are due to low Reynolds number. For Reynolds numbers typical of laboratory experiments and direct numerical simulations of turbulence the root-mean-square dispersion of marked particles is changed from the Langevin equation (i.e., infinite Reynolds number) prediction by up to about 50% at large times. Most of this change can be accounted for by the change in the Lagrangian integral time scale. It is also shown that Reynolds number effects in laboratory dispersion or Lagrangian turbulence measurements can cause significant errors (typically of order 50%) when the value of the Kolmogorov Lagrangian structure function constant C0 is estimated by fitting the predictions of the Langevin equation to these data. A value C0 = 7 is obtained by fitting the new model to the direct simulation data.
Some extensions to the Cercignani–Lampis gas–surface scattering kernel
Authors: Lord R. G.
Published: July 2002

The Cercignani–Lampis gas–surface scattering kernel is extended to include two important cases not covered by the basic model. These are (a) diffuse scattering with partial energy accommodation, and (b) accommodation of vibrational energy of a diatomic molecule with equally spaced energy levels. Both extensions are easily implemented in direct simulation Monte Carlo (DSMC) calculations. The results of some test calculations are presented.
Taylor dispersion in porous media. Determination of the dispersion tensor
Authors: Salles J. , Thovert J.-F. , Delannay R. , Prevors L. , Auriault J.-L. , Adler P. M.
Published: July 2002

In homogeneous porous media, the analytical expression of the dispersion tensor D* can be calculated by the method of moments and by a multiple scale expansion; the symmetric component of this tensor is identical in both cases. Numerically, D* can be computed by two methods, namely the B equation and random walks. The porous media are modeled as being spatially periodic; D* is determined as a function of the Péclet number for four types of unit cells: deterministic, fractal, random, and reconstructed. A systematic comparison is made with existing numerical and experimental data. The long time behavior, and its Gaussian limit, is documented.
A millimeter and submillimeter wavelength free-electron laser
Authors: Kirkpatrick D. A. , Bekefi G. , DiRienzo A. C. , Freund H. P. , Ganguly A. K.
Published: July 2002

Measurements of millimeter and submillimeter wavelength emission (240 GHz<ω/2π<470 GHz) from a free-electron laser are reported. The laser operates as a superradiant amplifier and without an axial guide magnetic field; focusing and transport of the electron beam through the wiggler interaction region are achieved by means of the bifilar helical wiggler field itself. Approximately 18 MW of rf power has been observed at a frequency of 470 GHz, corresponding to an electronic efficiency of 0.8%. Frequency spectra are measured with a grating spectrometer and show linewidths Δω/ω∼2%–4%. The experimental results are in very good agreement with nonlinear numerical simulations.
Absence of Dicke narrowing in x-ray laser plasmas?
Authors: Pollock E. L. , London Richard A.
Published: July 2002

Present x-ray laser plasmas are in the intermediate coupling regime (0.1<Γ<4, Γ≡Z2e2/kTa, with a the ion sphere radius), where the binary collision based arguments of low density plasma kinetic theory can be misleading. The difficulty of modeling the spectral output from neonlike lasers at wavelengths near 200 Å has led to the suggestion, based on a low density, electron screened, plasma model, that collisional (‘‘Dicke’’) narrowing may be important. Molecular dynamics results, which include ion collisions and screening effects, are presented here. They indicate that the free-particle Doppler approximation is still quite accurate for λ∼200 Å and Γ≲1. Collisional narrowing will become important at somewhat stronger couplings (Γ∼5) and at this wavelength the diffusion approximation is reasonable for Γ≳10. Collisional narrowing is found to be small even for the higher density (Γ≊4) nickel-like lasers operating near 45 Å.
Simulations of ultraintense laser–plasma interactions*
Authors: Wilks S. C.
Published: July 2002

The interaction of ultraintense, short pulse lasers with a preformed plasma is investigated using particle-in-cell (PIC) computer simulations. For this interaction regime, the electron motion in the presence of the intense light wave is strongly relativistic. Due to the extremely large light pressure associated with such pulses, a deep depression at the critical surface is formed, which causes the absorption to increase as a function of time. The result is that a substantial amount of the laser energy is absorbed by hot electrons that transport into the overdense plasma. There is also a large inward acceleration of ions. Comparison of the present simulation results with data obtained from a current experiment is also presented.
Beam–plasma instabilities and the beam–plasma discharge
Authors: Kellogg P. J. , Boswell R. W.
Published: July 2002

Using a new electron gun, a number of measurements bearing on the generation of beam–plasma discharge (BPD) in WOMBAT (waves on magnetized beams and turbulence) [R. W. Boswell and P. J. Kellogg, Geophys. Res. Lett. 10, 565 (1983)] have been made. A beam–plasma discharge is an rf discharge in which the rf fields are provided by instabilities [W. D. Getty and L. D. Smullin, J. Appl. Phys. 34, 3421 (1963)]. The new gun has a narrower divergence angle than the old, and comparison of the BPD thresholds for the two guns verifies that the BPD ignition current is proportional to the cross-sectional area of the plasma. The high-frequency instabilities, precursors to the BPD, are identified with the two Trivelpiece–Gould modes [A. W. Trivelpiece and R. W. Gould, J. Appl. Phys. 30, 1784 (1959)]. Which frequency appears depends on the neutral pressure. The measured frequencies are not consistent with the simple interpretation of the lower frequency as a Cerenkov resonance with the low-Trivelpiece–Gould mode; it must be a cyclotron resonance. As is generally true in such beam–plasma interaction experiments, strong low-frequency waves appear at currents far below those necessary for BPD ignition. These low-frequency waves are shown to control the onset of the high-frequency precursors to the BPD. A mechanism for this control is suggested, which involves the conversion of a convective instability to an absolute one by trapping of the unstable waves in the density perturbations of the low-frequency waves. This process greatly reduces the current necessary for BPD ignition.
Resonant ion acceleration by oblique magnetosonic shock wave in a collisionless plasma
Authors: Ohsawa Yukiharu
Published: July 2002

A magnetosonic shock wave propagating obliquely to a magnetic field is studied by theory and simulation, with particular attention to the resonant ion acceleration (the vp×B acceleration) by the shock. Theoretical analysis based on a two-fluid model shows that, in the laminar shock, the electric field strength in the direction normal to the wave is about (mi/me)1/2 times larger for the quasiperpendicular shock than that for the quasiparallel shock, which is a reflection of the fact that the width of the quasiperpendicular shock is much smaller than that of the quasiparallel shock. Time evolution of a totally self-consistent magnetosonic shock wave is studied by using a 2 1/2 -dimensional fully relativistic, fully electromagnetic particle simulation with full ion and electron dynamics. Even the low Mach number shock wave can significantly accelerate some ions by the vp×B acceleration. The resonant ion acceleration occurs more strongly in the quasiperpendicular shock, because the magnitude of this acceleration is proportional to the electric field strength.
Stability properties of relativistic shock waves: Basic results
Authors: Russo G. , Anile A. M.
Published: July 2002

The relativistic extensions of the stability properties of shock waves in classical gasdynamics are derived and studied in detail. In particular, the shock front instability resulting from the spontaneous emission of acoustic waves is thoroughly investigated.
Ion-acoustic solitons in a cylindrical plasma-loaded waveguide
Authors: Ghosh B. , Das K. P.
Published: July 2002

Nonlinear behavior of ion-acoustic waves propagating along a highly nonisothermal magnetized plasma filled cylindrical waveguide is investigated. A Korteweg–de Vries equation is derived to describe the weakly nonlinear behavior of the waves. The effects of a finite boundary on the propagation of ion-acoustic solitons are analyzed.
Self-similar, surfactant-driven flows
Authors: Jensen O. E.
Published: July 2002

Consider a dilute, insoluble surfactant monolayer on the free surface of a thin viscous film. A gradient in surfactant concentration generates a gradient in surface tension, driving a flow that redistributes the surfactant so that these gradients decay. The nonlinear evolution equations governing such flows, derived using lubrication theory, have previously been shown to admit a set of simple similarity solutions representing the spreading of a monolayer over an uncontaminated interface. Here, a much more general class of similarity solutions is considered, and a transformation is identified reducing the governing partial differential equations to a set of nonlinear ordinary differential equations, the solutions of which correspond to integral curves in a two-dimensional phase plane. This allows the construction of solutions to a wide range of problems. Many new solutions are revealed, including one that cannot be determined by simpler techniques, namely the closing of an axisymmetric hole in a monolayer, the radius of which is shown to be proportional to (−t)δ as t→0−, where δ≊0.807 41; this solution corresponds to a heteroclinic orbit in the phase plane.
Effects of intrinsic three-dimensionality on the drag characteristics of a normal flat plate
Authors: Najjar F. M. , Vanka S. P.
Published: July 2002

A three-dimensional direct numerical simulation of the wake of a flat plate held normal to a free stream has been conducted for a Reynolds number of 1000, using a high-order finite-difference scheme. The calculated flow structures and the coefficient of drag are shown to be markedly different from those obtained from an equally resolved two-dimensional simulation. The three-dimensional simulation is able to account for the intrinsic three-dimensionality that develops beyond a certain critical Reynolds number (∼200). The time-averaged drag predicted by the three-dimensional simulation is in good agreement with the experimental data, and also captures a low-frequency time variation that is seen in the experiments.
On depression of nonlinearity in turbulence
Authors: Tsinober A. , Ortenberg M. , Shtilman L.
Published: July 2002

A comparison is made of the behavior of nonlinearities in regions dominated by enstrophy and strain. It is shown that nonlinear processes like enstrophy production (and many others) are strongly depressed in regions dominated by enstrophy as compared to those dominated by strain.
Optimal perturbations for boundary layers subject to stream-wise pressure gradient
Authors: Corbett Peter , Bottaro Alessandro
Published: July 2002

Configurations of perturbation velocity which optimally excite an algebraic growth mechanism in the Falkner–Skan boundary layer are studied using a direct–adjoint technique. The largest transient amplification is obtained by stream-wise oriented vortices, in agreement with previous results for the Blasius boundary layer. Adverse pressure gradient is found to increase the resulting growth, the reverse is true for accelerated flows. It is shown that optimally excited algebraic mechanisms are capable of competition with optimally excited Tollmien–Schlichting waves in super-critical flows before succumbing to viscous damping. Disturbances optimized for maximal amplification over shorter periods are generally oblique and can experience significant transient growth; it is argued that they should not be dismissed when searching for rapidly growing perturbations which may preferentially induce early transition. Optimal disturbances transform into streaks downstream of their inception, attesting to the ubiquity of these flow structures.
Interaction of a density modulated electron beam with a magnetized plasma: Emission of whistler waves
Authors: Krafft C. , Matthieussent G. , Thévenet P. , Bresson S.
Published: July 2002

Whistler wave excitation in a magnetized laboratory plasma by a density modulated electron beam is studied for frequency modulation below, but in the range of, the electron gyrofrequency. When the beam velocity differs from the phase velocity of the whistler at the frequency modulation of the beam, a whistler wave, and, by Čerenkov emission, a beam wave at the same frequency are excited as single poles. When both velocities are equal, a resonance occurs leading to a maximum in the emission of whistler waves. The experiment performed in a magnetized plasma (np≊1011 cm−3, Te≊0.2 eV, B≊100 G) with a modulated electron beam (nb≊109 cm−3, Eb≊300 eV) is in agreement with a simple model which predicts the characteristics of the excited waves.
Kinetic to thermal energy transfer and interpenetration in the collision of laser-produced plasmas
Authors: Chenais-Popovics C. , Renaudin P. , Rancu O. , Gilleron F. , Gauthier J.-C. , Larroche O. , Peyrusse O. , Dirksmöller M. , Sondhauss P. , Missalla T. , Uschmann I. , Förster E. , Renner O. , Krousky E.
Published: July 2002

An experimental and numerical analysis of the collision of two plasmas produced from laser-exploded Al/Al and Al/Mg pairs of foils is presented. Various imaging and spectroscopic x-ray techniques have been used to diagnose the collision over a broad range of intertarget distances and laser intensities. Ion temperatures in the 10 keV range have been measured from Doppler broadening. Electron temperatures and densities have been deduced from line ratios and interpenetration distances have been determined by the spatial extent of Mg and Al x-ray lines. Eulerian multifluid simulations have been developed and coupled to atomic physics postprocessing. The comparison of the measurements with these simulations shows that interpenetration prevails at large intertarget distances and high laser intensities; kinetic to thermal energy transfer then takes place on a ∼200-μm wide region and during ∼150 ps.
Progress in resolving power and particle control issues for the International Thermonuclear Experimental Reactor
Authors: Post D. , Janeschitz G. , Kukushkin A. , Pacher H. , Sugihara M. , Mandrekas J. , Stacey W.
Published: July 2002

Recent tokamak divertor experiments with “detached” and “partially detached” divertor regimes show that a major portion of the heating power can be radiated to the walls to reduce the peak heat loads on divertor plates and that a combination of fueling and pumping can control the plasma density and exhaust impurities such as He. Tokamak transport codes and divertor modeling codes have been developed that can reproduce and predict the major features of these experiments. The combination of these recent experiments and the use of the models to extrapolate to ITER have led to the development of a concept for the International Thermonuclear Experimental Reactor [R. Aymar, Fusion Technol. 30, 397 (1996)] power and particle control system, which relies upon a single null “vertical target” divertor with gas and pellet fueling and active pumping. The experiments indicate that energy confinement can be adversely affected if the recycling neutrals and impurities are not well confined in the divertor, so that efficient confinement of neutrals in the divertor is a key feature of the divertor design.
Nonlinear dynamics of a charged dust grain in a plasma
Authors: Elskens Yves , Resendes David P. , Mendonça J. T.
Published: July 2002

For an arbitrary monotonic charging function, the dynamics of a dust grain is dissipative and energy is a Liapunov function. In an arbitrary external potential two types of equilibria exist. The first type, with uncharged grain, is always unstable. The second type of equilibrium, admitting states of both positive and negative charge, can be marginally stable; stability depends on the local potential. Under spatially uniform (constant or time-dependent) potentials, motion is free while the charge adapts to the potential. For a spatially oscillating potential, the phase space is that of the simple pendulum with one additional degree of freedom, the charge. Dissipation in the charging process forbids periodic behavior and ensures the existence of attractors: A grain is at stable equilibrium only when charged positively and trapped in a potential well, or when charged negatively on top of a hill. The small oscillations near a stable equilibrium decay weakly, and the grain charge oscillates at twice the oscillation frequency.
Predicting temperature and density profiles in tokamaks
Authors: Bateman Glenn , Kritz Arnold H. , Kinsey Jon E. , Redd Aaron J. , Weiland Jan
Published: July 2002

A fixed combination of theory-based transport models, called the Multi-Mode Model, is used in the BALDUR [C. E. Singer et al., Comput. Phys. Commun. 49, 275 (1988)] transport simulation code to predict the temperature and density profiles in tokamaks. The choice of the Multi-Mode Model has been guided by the philosophy of using the best transport theories available for the various modes of turbulence that dominate in different parts of the plasma. The Multi-Mode model has been found to provide a better match to temperature and density profiles than any of the other theory-based models currently available. A description and partial derivation of the Multi-Mode Model is presented, together with three new examples of simulations of the Tokamak Fusion Test Reactor (TFTR) [K. M. McGuire et al., Phys. Plasmas 2, 2176 (1995)]. The first simulation shows the strong effect of recycling on the ion temperature profile in TFTR supershot simulations. The second simulation explores the effect of a plasma current ramp—where the plasma energy content changes slowly on the energy confinement time scale. The third simulation shows that the Multi-Mode Model reproduces the experimentally measured profiles when tritium is used as the hydrogenic isotope in L-mode (low confinement mode) plasmas.
Oblique whistler waves generated in cold plasma by relativistic electron beams
Authors: Ciurea-Borcia Rodica , Matthieussent Gilles , Le Bel Edouard , Simonet Françoise , Solomon Jacques
Published: July 2002

Parallel and oblique propagation of whistler waves generated by relativistic electron beams are examined. From the general dispersion equation one derives the analytical formula for the linear growth rate in the relativistic case. The growth rate is computed for realistic plasma parameters, using two distinct distribution functions for the hot electron population. The results of the present paper can explain phenomena occurring in space plasmas where relativistic electrons are present.
Interferometric measurement of the nonlinear index of refraction, n2, of CdSxSe1−x-doped glasses
Authors: Olbright G. R. , Peyghambarian N.
Published: July 2002

A novel technique, which employs a modified Twyman–Green interferometer, is used to measure the nonlinear index of a CdS0.9Se0.1-doped glass at different wavelengths in the vicinity of the band gap at room temperature. The measured n2 values for the doped glass are compared with calculated values obtained by Kramers–Kronig transformation of the measured Δα(λ)=α(I1,λ)−α(I2,λ). A good agreement is achieved between the measured nonlinear dispersion and that obtained through the Kramers–Kronig relations.
E
0+Δ0 transitions in GaSb/AlSb quantum wells
Authors: Forchel A. , Cebulla U. , Tränkle G. , Ziem U. , Kroemer H. , Subbanna S. , Griffiths G.
Published: July 2002

We have observed optical transitions between the first subbands of the conduction band and the split-off valence band in GaSb/AlSb quantum well structures. The well width dependence of the emission energies is traced to quantization in the conduction band and in the split-off band. By comparison with data for the band-edge transitions the effective Δ0 gaps is the quantum wells are determined. Contrary to previous calculations the Δ0 gap energies are almost independent of the well width.
Optical nonlinearity in mercury telluride
Authors: Wolff P. A. , Yuen S. Y. , Harris K. A. , Cook J. W. , Schetzina J. F.
Published: July 2002

Mercury telluride is shown to have the largest known third-order nonlinear optic susceptibility with response time in the picosecond range. At 10.6 μm and T=300 K, χ(3)=1.6×10−4 esu. The response time, estimated from the dispersion of χ(3), is 5 ps. The effect is attributed to interband population modulation. It does not saturate below 1 MW/cm2.
Multichannel waveguide junctions for guided-wave optics
Authors: Kapon Eli , Thurston R. N.
Published: July 2002

We propose and analyze a new class of multichannel optical waveguide junctions. These junctions consist of a multimode channel waveguide that branches into several single-mode channels. We show that such waveguide junctions, when properly designed, can route each of the spatial modes of the multimode waveguide into a different single-mode channel. These waveguide junctions should be useful in selective mode excitation, routing, switching, modulation, and wavelength multiplexing/demultiplexing of guided waves, as well as for mode control in semiconductor lasers.
Monolithic integrated InGaAlAs/InP ridge waveguide photodiodes for 1.55 μm operation grown by molecular beam epitaxy
Authors: Cinguino P. , Genova F. , Rigo C. , Cacciatore C. , Stano A.
Published: July 2002

The monolithic integration of a low loss InGaAlAs ridge waveguide with a low leakage InGaAs photodiode is demonstrated. The structure has been grown by molecular beam epitaxy on an n+-InP substrate, using an InGaAlAs layer with a band gap of 1.29 μm, suitable for waveguiding at 1.55 μm wavelength. Absorption of the guided light is provided by leaky coupling from the InGaAlAs guiding layer into the higher index InGaAs absorbing region containing a p/n junction. The devices showed external quantum efficiencies as high as 20% for operation at 1.55 μm wavelength. This is the first demonstration of a monolithic integrated waveguide device in the InGaAlAs/InP material system.
Near-ideal Schottky barrier formation at metal-GaP interfaces
Authors: Brillson L. J. , Viturro R. E. , Slade M. L. , Chiaradia P. , Kilday D. , Kelly M. K. , Margaritondo G.
Published: July 2002

Soft x-ray photoemission measurements of ultrahigh-vacuum-cleaved GaP (110) surfaces with In, Al, Ge, Cu, and Au overlayers reveal Fermi level stabilization over a wide energy range and a near-ideal correlation between Schottky barrier height and metal work function. Coupled with recent findings for InAs (110) and InxGa1−xAs (100) (x>0) surfaces, these results demonstrate that Fermi level pinning in a narrow energy range is not representative of metal/III-V compound semiconductor interfaces.
Magnetic field sensor for cryogenic applications
Authors: Heinemann K. , Bärner K.
Published: July 2002

A new Hall-signal probe, based on amorphous (Fe100−xMnx)75P15C10 compounds, is described. The device is suitable for magnetic fields up to 1.5 T and the Hall coefficient is independent of temperature in the range 4.2 K≤T≤300 K.
Photothermal detection for light-scattering material by laser interferometry
Authors: Chen L. , Zhang S. Y.
Published: July 2002

A highly sensitive photothermal scheme is described, in which the photothermally induced refractive index variation is measured by a specially designed interferometry. The setup is very simple and stable in facilitating practical applications. It can be used for light-scattering samples, as well as other state samples. Some experiments for detection of both periodic and nonperiodic photothermal refractive index variation are performed.
Thin-film photoconductor-electroluminescent memory device with a high brightness and a wide and stable hysteresis
Authors: Thioulouse P. , Gonzalez C. , Solomon I.
Published: July 2002

An improved thin-film photoconductor-electroluminescent memory and display device is described, which integrates an optimized ZnS:Mn active layer, Ta2O5 insulating films, and a-Si1−xCx:H photoconducting material. The performance with a 1-kHz sinewave excitation is an hysteresis width of ≂25 V, an on luminance of ≂650 cd/m2, and an off luminance of ≂0.1 cd/m2. The memory effect shows no degradation over an estimated operating time of 2000 h. The electrical on switching time is shorter than 10 μs. The performance of a full-size panel based on this structure is briefly discussed.
Dynamics of microfabricated electronic neural networks
Authors: Schwartz D. B. , Howard R. E. , Denker J. S. , Epworth R. W. , Graf H. P. , Hubbard W. , Jackel L. D. , Straughn B. , Tennant D. M.
Published: July 2002

We have studied the dynamics of a totally interconnected network of nonlinear amplifiers by building model electronic circuits using dense arrays of resistors and discrete amplifiers. Such models have been discussed recently in the context of spin glasses and neural networks. Even without optimization for speed, these circuits easily reproduce and extend the results of computer simulations in considerably less time.
Superior characteristics of thermal oxide layers grown on amorphous silicon films
Authors: Wu Ching-Yuan , Chen Chiou-Feng
Published: July 2002

Thermal oxide layers grown on polycrystalline and amorphous silicon films have been analyzed and compared by using scanning electron microscope (SEM) photographs, ramp-voltage-stressed current-voltage (I-V) measurements, and constant current stress. The asperity effect observed from SEM photographs and the ramp-voltage-stressed I-V technique is found to be less serious for the thermal oxides grown on the amorphous silicon films, resulting in a smaller leakage current and a larger electron fluence endurance. These superior characteristics enable the amorphous silicon to be a good candidate for further scaled nonvolatile memory device applications.
High-mobility two-dimensional electron gas structure for modulation-doped GaAs transistors
Authors: Christou A. , Varmazis K. , Hatzopoulos Z.
Published: July 2002

Utilizing two spacer regions of AlxGa1−xAs (x=0.41) and an intervening superlattice region of ten periods of GaAs/AlGaAs, 100 Å per period, an optimization of the electron mobility and concentration was obtained. An electron mobility of 131 000 cm2/V s was obtained at 77 K with an electron sheet concentration of 1.2×1012 cm−2.
Space-charge-limited current in a miniaturized quadrupole channel
Authors: Thomae R. W. , Siebenlist F. , van Putten A. E. , van Amersfoort P. W. , Klein H. , Schempp A. , Weis T.
Published: July 2002

We present measurements on the transport of low-energy ions through a miniaturized electrostatic quadrupole channel. These are done at a zero-current phase advance per cell of 60°. The limiting current is 50% smaller than is calculated with the Kapchinsky–Vladimirsky equations. This reduction is attributed to mismatch and misalignment, which have a pronounced influence in a miniaturized channel.
Reduction of spectral linewidth in AlGaAs/GaAs distributed feedback lasers by a multiple quantum well structure
Authors: Noda Susumu , Kojima Keisuke , Kyuma Kazuo , Hamanaka Koichi , Nakayama Takashi
Published: July 2002

We demonstrate the reduction of the spectral linewidth in AlGaAs/GaAs distributed feedback lasers by a multiple quantum well structure for the first time. The spectral linewidth-output power product was 54 MHz mW and was eight times smaller than that of conventional double heterostructure distributed feedback lasers. The narrowest spectral linewidth was 10.5 MHz at 5 mW.
Segregation and drift of arsenic in SiO2 under the influence of a temperature gradient
Authors: Celler G. K. , Trimble L. E. , West K. W. , Pfeiffer L. , Sheng T. T.
Published: July 2002

We have found that arsenic implanted into SiO2 segregates at high temperatures into As-rich spherical inclusions of 50–500 Å in diameter, provided that there is no free oxygen in the SiO2 and the initial As concentration exceeds 1 at. %. The phase separation suppresses the diffusion of arsenic, even at temperatures as high as 1400 °C. We have discovered, however, that the As-rich inclusions can be easily moved in a temperature gradient. They migrate towards the heat source at a rate of 2300 Å/h in a gradient of 0.14 °C/μm, at 1405 °C, permitting their efficient removal from the oxide and into silicon.
Thermal piston model for the optoacoustic effect: Sound generation in an optically thick gas
Authors: Stewart R. B. , Diebold G. J.
Published: July 2002

At high concentrations of an infrared absorbing gas, the optical absorption length for the incident radiation can become small compared with the thermal diffusion length in the gas. A description of the optoacoustic effect consequently must include thermal conduction of heat to the cell window since sound generation takes place in a thin layer of gas adjacent to the entrance window. A piston model is given here for the optoacoustic effect generated in a highly absorbing gas; in addition, experiments are reported that show new phase and amplitude dependences of the acoustic signal on gas concentrations, and modulation frequency.
Between explosive crystallization and amorphous regrowth: Inhomogeneous solidification upon pulsed-laser annealing of amorphous silicon
Authors: Bruines J. J. P. , van Hal R. P. M. , Koek B. H. , Viegers M. P. A. , Boots H. M. J.
Published: July 2002

Si amorphized by Cu implantation has been irradiated by spatially uniform pulses of 7.5 ns duration from a frequency-doubled neodymium:yttrium aluminum garnet laser. After irradiation the samples were examined by cross-section transmission electron microscopy. A laterally random pattern of polycrystalline Si patches was found imbedded in amorphous material. At low-energy densities a considerable fraction of the regrown Si was polycrystalline. With increasing energy density the amount of polycrystalline Si decreased, both at the surface and in total. These results are discussed in terms of the time available for the nucleation of polycrystalline Si at a liquid-solid interface and the temperature profile in both the liquid and the solid material.
Fabrication and microwave measurement of a space harmonic monolithic structure
Authors: Krowne Clifford M. , McCarthy Daniel
Published: July 2002

Theory, engineering design, fabrication, and experimental test of the first completely monolithic grating amplifier realized in silicon are described. Experimental results are presented for frequencies between 0.1 and 2.0 GHz at 300 K for the device, referred to as the solid state space harmonic amplifier structure. Electronic gain is about 1.5 dB/mm with a cold circuit loss of 4.6 dB/mm for the 200-μm-long interaction region device.
Programmed magnetic field applied liquid encapsulated Czochralski crystal growth
Authors: Ozawa Shoichi , Kimura Tadashi , Kobayashi Junji , Fukuda Tsuguo
Published: July 2002

We have developed a programmed magnetic field applied liquid encapsulated Czochralski crystal growth technique which produces a homogeneous impurity distribution along the growth axis of the crystal. In this technique the magnetic field strength is controlled in a programmed manner during growth. The results of growing iron-doped InP crystal with this technique are presented.
Oscillation frequency tuning characteristics of fiber-extended-cavity distributed-feedback lasers
Authors: Liou K.-Y. , Ku R. T. , Shen T. M. , Anthony P. J.
Published: July 2002

Stable narrow-linewidth (<100 kHz) operation has been demonstrated for a fiber-extended-cavity distributed-feedback (EC DFB) laser emitting at 1.55 μm wavelength. We describe the observed oscillation frequency tuning characteristics of the laser obtained by controlling the temperature and injection current. The effects of distributed grating reflection and continuous frequency tuning schemes are examined for both the EC DFB laser and for the case of an EC DBR (distributed Bragg reflector) laser.
Optical signal selection with a constant gain and a gain bandwidth by a multielectrode distributed feedback laser amplifier
Authors: Magari Katsuaki , Kawaguchi Hitoshi , Oe Kunishige , Nakano Yoshinori , Fukuda Mitsuo
Published: July 2002

Optical demultiplexing characteristics are studied using a multielectrode distributed feedback laser amplifier. The gain maximum frequency is tunable over 20.6 GHz with a constant insertion gain (9.7±1.2 dB) and a constant gain bandwidth (2.9 GHz), without any mode jump, by changing the driving current of the divided two electrodes. A single optical signal can be selected from two optical inputs separated by 15.4 GHz with an extinction ratio of better than −20 dB.
Chirped gratings for efficient coupling into nonlinear waveguides
Authors: Moshrefzadeh R. , Svensson B. , Xu Mai , Seaton C. T. , Stegeman G. I.
Published: July 2002

We show experimentally that chirped gratings can be used to obtain high coupling efficiencies into waveguides containing media with an intensity-dependent refractive index.
Nonlinear excitonic optical absorption in GaSb
Authors: Fox A. M. , Maciel A. C. , Ryan J. F. , Kerr T.
Published: July 2002

We have measured the saturation of optical absorption in GaSb at wavelengths close to the band gap, and have determined the nonlinear absorption (α2) and refraction (n2) coefficients. At liquid-helium temperature a sharp free-exciton absorption line is observed which saturates with increasing incident laser intensity; we obtain values ‖α2‖=70 cm W−1 and ‖n2‖≊0.2 cm2 kW−1. At room temperature we do not observe a well-defined exciton; saturation of the residual interband absorption occurs at much higher intensity, and it is found to be obscured by strong thermal effects.
Thermally stimulated resonant current in AlGaAs/GaAs triple barrier diodes
Authors: Nakagawa T. , Fujita T. , Matsumoto Y. , Kojima T. , Ohta K.
Published: July 2002

Thermally stimulated resonant current peaks are observed in Al0.4Ga0.6As/GaAs triple barrier diodes. These current peaks are interpreted as resonant tunnelings from the first excited electron subband in the first well to the first excited subband and to the second excited subband in the second well. The activation energies for these resonance peaks are measured. The results imply that in the substrate-side well there is a large amount of excess electrons to compensate the positive charge of silicon atoms segregated into the structure during the growth.
Low-loss optical waveguides in lithium tantalate by vapor diffusion
Authors: Eknoyan O. , Yoon D. W. , Taylor H. F.
Published: July 2002

Planar and channel optical waveguides have been produced in Y-cut LiTaO3 substrates by zinc diffusion from the gaseous phase at 800 °C. Prism coupler measurements on planar waveguides diffused for 6 h indicate effective index changes of 0.0063 and 0.0033 for TE and TM polarizations, respectively, with effective diffusion depths of 3.5 and 3.9 μm for the two polarizations. Losses in channel waveguides at 0.633 μm wavelength were 1.0±0.2 dB/cm for TE polarized fields, as compared with 4.7±1.0 dB/cm measured on companion samples produced by the conventional Ti indiffusion process at 1150 °C. Electro-optic modulation has been demonstrated in channel waveguide interferometers produced by this technique. Based on electron microprobe analysis, a surface Zn concentration of ∼1.3×1021 cm−3 has been determined.
Concentration profile and effective concentration in acceptor hydrogenation experiments
Authors: Pan Samuel Cheng-Sheng , Sah Chih-Tang
Published: July 2002

The effective dopant concentration determined from the capacitance minimum in the high-frequency capacitance-voltage curve is related to the actual majority-carrier density profile through a simple integration formula. Based on this relationship, the nonuniform substrate doping effect on the analysis of group-III acceptor hydrogenation experiments in silicon is examined. It is found that the procedure in determining the kinetic coefficients by fitting the effective dopant concentration versus avalanche injection or annealing time curves is appropriate if the hydrogen concentration is assumed uniform throughout the semiconductor surface space-charge layer.
On-line plasma diagnostic by neutral atom time of flight analysis
Authors: Dose V. , Verbeek H.
Published: July 2002

Elementary procedures of linear algebra and numerical integration are combined for processing neutral atom time of flight spectra from a tokamak plasma. The method presented provides for on-line information about total neutral particle flux, mean energy, wall erosion rates, etc. at a time resolution of a single time of flight cycle.
Use of angle-dependent photoemission for atom profiling: Au on compound semiconductors
Authors: Shapira Yoram , Xu F. , Hill D. M. , Weaver J. H.
Published: July 2002

We present studies of Au film formation on the III-V compound semiconductors GaAs and InSb based on polar-angle-dependent x-ray photoelectron spectroscopy. The results highlight the power of this technique as a nondestructive tool for atom profiling. The Au overlayer is highly heterogeneous due to disruption of the original surface and significant anion segregation in Au. Although GaAs and InSb show common behavior, significant differences are observed because the anion–cation bond strength determines the extent of the surface disruption and semiconductor atom solid solubilities in Au dominate the segregation patterns in each system. We present a model of the overlayer structure, based on thermodynamic considerations, which shows very good quantitative agreement with the observed profiles.
Yield dependency on length of AlGaAs/GaAs second-order distributed feedback lasers with cleaved facets
Authors: Hirata Shoji , Ohata Toyoharu , Yamamoto Tadashi , Kojima Chiaki
Published: July 2002

The effect of length on the yield of second-order distributed feedback lasers with cleaved facets capable of operating in a single longitudinal mode and on their characteristics has been studied experimentally. The optimum length of 200 μm was determined in reference to the coupling coefficient and the end-facet reflectivity. A yield of more than 70% was obtained for lasers 200 μm in length capable of operating at a level of at least 10 mW and over.
Resonant Raman scattering of hydrogenated amorphous carbon: Evidence for π-bonded carbon clusters
Authors: Ramsteiner M. , Wagner J.
Published: July 2002

Resonant Raman spectroscopy has been used to study amorphous hydrogenated carbon films. For films containing both sp2 and sp3 bonded carbon a well-defined high-frequency shift of the main Raman peak is observed with increasing exciting photon energy. This shift is interpreted in terms of scattering from π-bonded carbon clusters which is resonantly enhanced for incident photon energies approaching the π–π* resonance.
High-speed light valve using an amorphous silicon photosensor and ferroelectric liquid crystals
Authors: Takahashi N. Shin-ichi , Asada Hideki , Miyahara Masaki , Kurita Shoichi , Kuriyama Hiroyuki
Published: July 2002

A novel high-speed response light valve composed of a hydrogenated amorphous silicon (a-Si:H) photosensor and a chiral smectic C phase liquid crystal is presented for the first time. This device is optically addressed. The switching between on and off states is caused by reversing the polarity of the applied voltage across the liquid crystal due to the photocurrent from the a-Si photosensor. The response time measured is about 400 μs. The switching speed of this device is one to two orders of magnitude faster than that of the nematic liquid-crystal light valve. This device can be applied to optical bistable devices without optical feedback, using an electro-optic memory effect of the ferroelectric liquid crystal.
Electric field and infrared-induced recovery of metastability in amorphous hydrogenated silicon
Authors: Bhattacharya E. , Pankove J. I. , Deb S. K.
Published: July 2002

In this letter we investigate the difference between the bond breaking and the charge trapping model of the light-induced effect in amorphous hydrogenated silicon (a-Si:H). We also report the partial recovery from the light-induced effect in p-i-n solar cells by infrared illumination in the presence of an electric field.
Ion-chain interaction in keV ion-beam-irradiated polystyrene
Authors: Calcagno L. , Foti G. , Licciardello A. , Puglisi O.
Published: July 2002

Molecular weight distribution has been measured in monodisperse polystyrene film (MW=9 000 amu) after ion bombardment, in the ion fluence range 1011–1013 ions/cm2. The chosen beams are 100 keV He, 200 keV Ne, and 400 keV Ar. The experimental data have been interpreted in terms of a simple statistical model for cross-links. The chemical yield is found to be very high and equal to 0.30, about a factor of 10 higher than the values given in the literature for gamma irradiation [M. Dole, in The Radiation Chemistry of Macromolecules (Academic, New York, 1973), Vol. 2, Chap. 5, p. 57].
GaAs-GaAlAs graded-index separate confinement heterostructure laser diodes selectively grown by molecular beam epitaxy on SiO2-masked substrates
Authors: Hong J. M. , Wu M. C. , Wang S. , Wang W. I. , Chang L. L.
Published: July 2002

The GaAs-GaAlAs graded-index separate confinement heterostructure was grown selectively by molecular beam epitaxy on a SiO2-masked GaAs (100) substrate. The stripe windows on the SiO2 mask were 10 μm in width and were oriented along [011̄] direction. The laser diodes thus fabricated lased in a single longitudinal mode with a side mode suppression ratio of 95:1. Both the longitudinal mode and the single-lobe far-field pattern were stable up to 4Ith.
Effect of deposition process on the thin-film ZnS/p-Si interface
Authors: Sands D. , Brunson K. M. , Thomas C. B. , Reehal H. S.
Published: July 2002

Thin films of ZnS have been deposited on p-Si by evaporation, radio-frequency sputtering, and magnetron sputtering to form metal-insulator-semiconductor structures. The 1 MHz admittance-voltage characteristics of each have been compared for a qualitative study of the ZnS/p-Si interface. It is shown that radio-frequency sputtering results in Fermi-level pinning, which is ascribed to the presence of silicon dangling bonds caused by radiation damage. It is argued that this damage is advantageous for ZnS/p-Si electroluminescent diodes.