bluuebunny/crossref_metadata_2025 huggingface dataset:
Adiabatic nucleation in the liquid–vapor phase transition
Authors: de Sá Elon M. , Meyer Erich , Soares Vitorvani
Published: July 2002

The fundamental difference between classical (isothermal) nucleation theory (CNT) and adiabatic nucleation theory (ANT) is discussed. CNT uses the concept of isothermal heterophase fluctuations, while ANT depends on common fluctuations of the thermodynamic variables. Applications to the nonequilibrium liquid to vapor transition are shown. However, we cannot yet calculate nucleation frequencies. At present, we can only indicate at what temperatures and pressures copious homogeneous nucleation is expected in the liquid to vapor phase transition. It is also explained why a similar general indication cannot be made for the inverse vapor to liquid transition. Simultaneously, the validity of Peng–Robinson’s equation of state [D.-Y. Peng and D. B. Robinson, Ind. Eng. Chem. Fundam. 15, 59 (1976)] is confirmed for highly supersaturated liquids.
Growth rates of the m=0 mode for Bennett equilibria with varying radial density and temperature profiles
Authors: Stoltz P. H. , Oliver B. V.
Published: July 2002

The linear growth of axisymmetric (m=0) perturbations for various Bennett pinch equilibria are studied numerically with the ALEGRA-MHD code [A. C. Robinson, C. J. Garasi, T. A. Haill, R. L. Morse, and P. H. Stoltz, Proceedings of the 26th IEEE Conference on Plasma Science (IEEE, Piscataway, NJ, 1999), p. 306]. Growth rates are calculated for both skin and diffuse current profiles with varied density and temperature profiles. A destabilizing effect of radially increasing temperature profiles is presented. A factor of three increase in the growth rate over a constant-temperature equilibrium is noted for an equilibrium which is ten times hotter on the edge than at the core. A qualitative explanation is given in terms of the sound speed in the radial region where the mode resides.
Application of foil strain gauges in high pressure research
Authors: Wiśniewski Z. , Wiśniewski R. , Nowiński J. L.
Published: July 2002

Possibilities of the application of resistance foil strain gauges in high pressure research are discussed. In order to demonstrate such a possibility, the isothermal linear compressibility of selected metals, such as Al, Cu, and Fe, was measured with the use of foil strain gauges. The results obtained were compared with those given in the literature. Also, the possible effect of a protective foil on foil gauge properties subjected to high pressures was investigated. The experiments have shown that foil strain gauges are suitable for compressibility measurements and attain similar accuracy as wire strain gauges. The measuring method presented here was used to determine the compressibility of superionic glass given by the formula 0.4Agl-0.6(Ag2O–P2O5). It is concluded that the improved properties of foil strain gauges, in comparison with the wire ones, will result in better application possibilities of foil strain gauges in high pressure research.
Quantum reactive scattering calculations for the H+D2→HD+D reaction
Authors: Kendrick Brian K.
Published: July 2002

The results of accurate 3D quantum scattering calculations in symmetrized hyperspherical coordinates are reported for the H+D2(v,j)→HD(v′,j′)+D reaction at 64 values of total energy in the range 0.5–1.9 eV. Integral and differential cross sections are computed using the Boothroyd–Keogh–Martin–Peterson potential energy surface for all values of total angular momentum J⩽31. Several transition state resonances survive the sum over J and are observed in many of the fully converged state-to-state integral and differential cross sections. In some cases a series of resonances is observed. The energy spacings between many of the resonances are consistent with the energy spacings between the even or odd bending modes of the quantized transition states of H3.
Effects of open field line plasma on rotating magnetic field current drive in a field-reversed configuration
Authors: Milroy Richard D.
Published: July 2002

A numerical model has been used to study the effects that open field line plasma may have on the rotating magnetic field (RMF), when it is applied to a field-reversed configuration (FRC) for current drive. The model is a two-dimensional (r–θ) magnetohydrodynamic computer simulation. The RMF is found to be an extremely good particle pump, continuously sweeping plasma into the FRC from the outer region, and thus evacuating the space near the containment vessel wall. This effect can lead to a very low density near the wall, providing good thermal insulation. However, if there is a plasma source in the open field line region (such as outgassing from the containment vessel wall) capable of maintaining relatively low-density plasma, the RMF may be amplified in this region. While this effect may speed the rate of penetration, it also has a deleterious effect where excessive penetration leads to predictions of an internal structure that rotates slower than the RMF, and chaotic equilibrium.
3.5 W frequency-doubled fiber-based laser source at 772 nm
Authors: Champert P. A. , Popov S. V. , Taylor J. R.
Published: July 2002

A 3.5 W fiber-based laser source at 772 nm is demonstrated by using quasiphase-matched second-harmonic generation of a 40 dBm seeded ytterbium–erbium fiber amplifier in PPKTP. A 40% conversion efficiency is achieved across the entire output power range of the EDFA. No optical damage has been observed in the PPKTP over long-term high-power exposure.
Importance of random fields on the properties and ferroelectric phase stability of 〈001〉 oriented 0.7 Pb(Mg1/3Nb2/3)O3–0.3 PbTiO3 crystals
Authors: Viehland D. , Powers J. , Cross L. E. , Li J. F.
Published: July 2002

Temperature dependent dielectric constant measurements have been performed on 〈001〉 oriented 0.7 Pb(Mg1/3Nb2/3)O3–0.3 PbTiO3 crystals. These investigations have revealed an irreversible secondary transformation between a normal ferroelectric state and a relaxor ferroelectric state with increasing temperature. The results demonstrate that the anisotropy of the high performance piezocrystal state is only metastably locked in under application of field. Clearly, local random fields play a crucial role upon the ferroelectric phase stability and properties of 〈001〉 oriented piezocrystals.
Investigation of the emission mechanism in InGaN/GaN-based light-emitting diodes
Authors: Wang T. , Bai J. , Sakai S. , Ho J. K.
Published: July 2002

The exciton-localization effect and quantum-confine Stark effect (QCSE) on the performance of InGaN/GaN-based light-emitting diodes (LEDs) have been investigated with regard to indium mole fraction and well thickness by means of temperature-dependent and excitation-power-dependent photoluminescence measurements. The exciton-localization effect can be enhanced by increasing the indium mole fraction or increasing well thickness but up to 2.5 nm. The QCSE is monotonically enhanced with increasing indium concentration or well thickness. The output power of the LED can be increased by the enhanced exciton-localization effect; however, the QCSE has much stronger influence on the output power of LEDs than the exciton-localization effect, which should be taken into account for further improving the performance of InGaN/GaN-based LEDs.
The ground state of silylidene (H2C=Si), the silicon analog of vinylidene, from stimulated emission pumping and wavelength-resolved fluorescence spectroscopy
Authors: Smith Tony C. , Li Haiyang , Clouthier Dennis J.
Published: July 2002

The ground state vibrational energy levels of jet-cooled H2CSi and D2CSi have been studied by a combination of wavelength-resolved fluorescence and stimulated emission pumping (SEP) techniques. By taking advantage of the vibrational selection rules and Franck–Condon factors and selectively pumping upper state single vibronic levels, readily assignable low-resolution emission spectra were obtained. Higher resolution SEP spectra were recorded to give precise measurements of the vibrational band origins of many of the lower-lying vibrational levels. All of the vibrational frequencies, except for the Franck–Condon inactive CH asymmetric stretching mode, ν5, have been determined for both isotopomers. The CH2 rocking mode (ν6) is found to have a very low 263 cm−1 frequency in the ground state. The spectra are complicated by unexpected activity in the out-of-plane bending vibration.
Torsional diffusion Monte Carlo: A method for quantum simulations of proteins
Authors: Clary David C.
Published: July 2002

The quantum diffusion Monte Carlo (DMC) method is extended to the treatment of coupled torsional motions in proteins. A general algorithm and computer program has been developed by interfacing this torsional-DMC method with all-atom force-fields for proteins. The method gives the zero-point energy and atomic coordinates averaged over the coupled torsional motions in the quantum ground state of the protein. Application of the new algorithm is made to the proteins gelsolin (356 atoms and 142 torsions) and gp41-HIV (1101 atoms and 452 torsions). The results indicate that quantum-dynamical effects are important for the energies and geometries of typical proteins such as these.
Incessant acceleration of relativistic ions by an oblique shock wave
Authors: Usami Shunsuke , Hasegawa Hiroki , Ohsawa Yukiharu
Published: July 2002

Motions of nonthermal, fast ions in an oblique shock wave are studied theoretically and numerically. After the encounter with a shock wave, some of the fast ions get to move with it. Their energies then increase once in each gyroperiod. Their momenta parallel to the magnetic field also increase. Thus, these particles eventually escape, going away ahead of the wave. However, it is theoretically predicted that under certain circumstances, owing to relativistic effects, particles cannot go faster in the direction of the shock propagation than the wave. Some particles therefore cannot escape from the wave. Accordingly, the acceleration could be repeated indefinitely. This idea is examined by means of a one-dimensional, relativistic, electromagnetic, particle simulation code with full ion and electron dynamics. The simulations demonstrate that the repeated acceleration of relativistic ions does occur. The acceleration processes were observed to continue until the end of simulation run. Also, it is shown that as the theory predicts, a higher energy particle can gain a greater amount of energy.
Design of a magnetically shielded helium cryostat insert with a variable temperature regulated stage
Authors: Ridereau Xavier , Sing Marc Lam Chok , Bloyet Daniel
Published: July 2002

This note describes the design and realization of a liquid helium cryostat insert comprising a variable temperature regulated stage. The latter is magnetically shielded by a superconducting lead pot bathing in liquid helium. This apparatus is intended for the study of high Tc superconducting films and superconducting quantum interference devices submitted to different applied magnetic fields for temperatures ranging from 50 to 100 K.
Efficient and stable operation of an Ar+-pumped continuous-wave ring laser from 505–560 nm using a coumarin laser dye
Authors: Jusinski Leonard E. , Taatjes Craig A.
Published: July 2002

A coumarin laser dye has been found to produce efficiencies and lifetimes comparable to those of the rhodamines. Coumarin 521 (coumarin 334) produces up to 400 mW of single frequency light (frequency width <1 MHz) at 520 nm in a ring laser when excited with 2.4 W of 457.9 nm light from an Ar+ ion laser. Operation with a 488 nm pump shows slightly lower efficiency. Dye lifetime to 75% full power has exceeded 1000 W h over a period of several months. Methanol and ethylene glycol are the only solvents required. This dye operates in a portion of the tuning range of a continuous-wave ring dye laser which is otherwise extremely difficult to access using an argon ion laser as the pump source. Used in conjunction with an external buildup cavity, 8–12 mW of 258 nm light is reliably produced for weeks at a time.
Laser ultrasonics for measurements of high-temperature elastic properties and internal temperature distribution
Authors: Matsumoto Takahiro , Nagata Yasuaki , Nose Tetsuro , Kawashima Katsuhiro
Published: July 2002

We show two kinds of demonstrations using a laser ultrasonic method. First, we present the results of Young's modulus of ceramics at temperatures above 1600 °C. Second, we introduce the method to determine the internal temperature distribution of a hot steel plate with errors of less than 3%. We compare the results obtained by this laser ultrasonic method with conventional contact techniques to show the validity of this method.
Vector magnetization imaging in ferromagnetic thin films using soft x-rays
Authors: Kim Sang-Koog , Kortright J. B. , Shin Sung-Chul
Published: July 2002

A magnetization vector M imaging using a transmission x-ray microscope with magnetic circular dichroism (MCD) contrast is demonstrated. MCD images through a semitransparent, 33-nm-thick Fe film are measured at the Fe L3 edge along three different x-ray propagation directions to determine all three components of the M. The transmission images clearly display the vector nature of complex microstructures, associated with the M reversal between oppositely oriented 180° domains, including not only 90° domains, a Néel wall-like structure, and an extended ripple structure, but also a striking feature of localized magnetization spirals with perpendicular components at their cores. These studies have important implications for applications of this technique to better understand the expected features as well as details of domain-wall structures.
Gyrokinetic calculations of the neoclassical radial electric field in stellarator plasmas
Authors: Lewandowski J. L. V. , Williams J. , Boozer A. H. , Lin Z.
Published: July 2002

A novel method to calculate the neoclassical radial electric field in stellarator plasmas is described. The method, which does not have the inconvenience of large statistical fluctuations (noise) of the standard Monte Carlo technique, is based on the variation of the combined parallel and perpendicular pressures on a magnetic surface. Using a three-dimensional gyro-kinetic δf code, the calculation of the radial electric field (Er) in the National Compact Stellarator Experiment [G. H. Neilson et al., Phys. Plasmas 7, 1911 (2000)] has been carried out. It is shown that a direct evaluation of Er based on a direct calculation of the radial particle flux is not tractable due to the considerable noise.
K-shell photoionizations in classical nonideal plasmas
Authors: Jung Young-Dae
Published: July 2002

Collective and plasma screening effects on photoionization cross sections from the 1s state of hydrogenic ions in classical nonideal plasmas are investigated. An effective pseudopotential model taking into account the collective and plasma screening effects is applied to describe the interaction potential in nonideal plasmas. The screened atomic wave function and energy eigenvalue for the ground state of the hydrogenic ion in classical nonideal plasmas are obtained by the Ritz variational method. The photoionization cross section is obtained by the acceleration form of the transition matrix element in order to investigate the collective and plasma screening effects on the interaction potential. The retardation and Coulomb correction effects are also considered in nonideal plasmas. The total correlation effect is obtained as a function of the nonideality plasma parameter, Debye length, and incident photon energy. The result shows that the collective effect significantly reduces the photoionization cross section. It is also found that the collective effect on the photoionization cross section is increased with increasing the incident photon energy.
Annealing effect of magnetic tunnel junctions with one FeOx layer inserted at the Al2O3/CoFe interface
Authors: Zhang Zongzhi , Cardoso Susana , Freitas P. P. , Wei P. , Barradas N. , Soares J. C.
Published: July 2002

Spin tunnel junctions with one interposed Fe oxide layer between the Al2O3 barrier (tAl=8–9 Å) and the top CoFe pinned layer show large tunneling magnetoresistance (TMR) values (39%) after 40 min anneal at 380 °C. The as-deposited TMR is low and does not increase until 350 °C (<10%), but then increases sharply, peaking at 380°C. Further anneals at this temperature (380 °C), lead to TMR decrease to 20% with a diffusion constant of 34 min. At 360 °C, the diffusion constant is about 60 min. Samples without this inserted FeOx layer show TMR<5% after prolonged anneals at 380 °C. The different techniques utilized to probe the barrier and electrode changes during the annealing processes indicate that from the initial Fe–FeOx layer, part of the Fe diffuses into the CoFe electrode, and the remaining FeOx probably decomposes into a pure interfacial Fe layer at high temperature, responsible for the large TMR. The observed TMR values and barrier parameters, seem consistent with a standard CoFe/Al2O3/CoFe barrier formed at high temperature.
Magnetic field generation in a plasma in the presence of an ultrashort laser pulse
Authors: Ferrante G. , Zarcone M. , Uryupin S. A.
Published: July 2002

The description of the Weibel instability linear stage for a plasma interacting with an ultrashort laser pulse is given. Pulse durations both smaller and larger than the inverse collision frequency of the thermal electrons are considered. In the latter case the pulse duration is smaller than the thermal electron heating time. The growth rate of the instability is derived and the possibility of a considerable quasistationary magnetic field amplification demonstrated.
Local grain orientation and strain in polycrystalline YBa2Cu3O7−δ superconductor thin films measured by Raman spectroscopy
Authors: Amer Maher S. , Maguire John , Cai L. , Biggers R. , Busbee J. , LeClair S. R.
Published: July 2002

We report direct measurements of local grain orientation and residual strain in polycrystalline, C-axis oriented thin YBa2Cu3O7−δ superconducting films using polarized Raman spectroscopy. Strain dependence of the Ag Raman active mode at 335 cm−1 was calibrated and used to measure local strain in the films. Our data showed that high quality films are associated with the connected path of uniform grain orientation (single crystal-like) across the film and uniform residual strain in the range of −0.3%. Nonuniform grain orientation or high angle grain boundaries and nonuniform local strains were associated with low quality films.
A low noise cryogenic preamplifier for the cosmic microwave background radiation anisotropy experiment
Authors: Oh E. S. , Sharp E. H. , Fixsen D. J. , Cheng E. S. , Inman C. A. , Silver C.
Published: July 2002

A cryogenic stage preamplifier for the TopHat experiment is built with InterFet NJ132L junction field effect transistors. We describe the testing procedure, screening, and fabrication of the six-channel preamplifier. It is attached to the LN2 shield and self-heats to 110 K with 20 mW total dissipation. The noise performance with grounded input is 7 nV root-mean-square (rms)/Hz at 1.5 Hz and 1 nV rms/Hz at 50 Hz.
Simultaneous measurement of changes in thickness and refractive index of weakly absorbing self-standing solid films using optical interferometry
Authors: Easwar N. , Fantini R. , Willis E.
Published: July 2002

A nondestructive optical interferometric method, which enables a direct and simultaneous measurement of small changes in both thickness and refractive index of thin films, is described. Optical interferometric methods are sensitive to the changes in the optical path length (the product of the refractive index and the physical thickness) through the film. Thus, when the film is subjected to changing environmental conditions such as changing temperature or humidity, it is a challenge to determine the change in thickness and the change in refractive index separately, using interferometry. By simultaneously monitoring two different sets of interference fringes, i.e., transmission and reflection fringes, we have been able to successfully address this challenge. Our measurements on well-characterized pedigree glass samples are presented. The results agree well with the expected values for these samples, supporting the feasibility of this characterization technique to new materials. Self-standing, transparent (weakly absorbing) films ranging in thickness from tens to hundreds of microns can be characterized from direct measurements.
An inertial range crossover in structure functions
Authors: Kerr Robert M. , Meneguzzi Maurice , Gotoh Toshiyuki
Published: July 2002

Experimental and numerical data within the traditional inertial subrange defined by the third-order structure function is used to study higher-order scaling exponents for the longitudinal and transverse structure functions. For 262<Rλ<3200, these exponents converge only over larger scales, r>rS, where rS is between η and λ and has an Rλ dependence. Below these scales, scaling exponents cannot be determined for any of the structure functions without resorting to procedures such as extended self-similarity (ESS). With ESS, different longitudinal and transverse higher-order exponents are obtained that are consistent with earlier results. The relationship of these statistics to derivative and pressure statistics, to turbulent structures and to length scales is discussed.
Spectroscopic constants and potential energy curves of Nb2 and Nb2+
Authors: Balasubramanian K. , Zhu Xiao Lei
Published: July 2002

Potential energy curves and spectroscopic constants for 45 low-lying electronic states of Nb2, 18 electronic states of Nb2+, and 2 low-lying states of Nb2− have been computed using the complete active space multiconfiguration self-consistent field followed by the multireference singles+doubles configuration interaction calculations that included up to 17 million configurations. The equilibrium distances (re), vibrational frequencies (ωe), and energy separations (Te) are reported. We have also computed the properties of the two lowest electronic states of Nb2−. Possible assignments are suggested for the recently observed fragmentation spectra and three-photon fragmentation spectra of Nb2+ as well as the spectra of Nb2. The dissociation energies and ionization potentials of Nb2 and Nb2+ as well as electron affinities of Nb2 are computed. The nature of bonding is discussed using the wave function composition and Mulliken population analysis.
Low-temperature orientational ordering and possible domain structures in C60 fullerite
Authors: Loktev V. M. , Pogorelov Y. G. , Khalack J. N.
Published: July 2002

Based on a simple model for the ordering of hexagons on a square planar lattice, an attempt is made to consider the possible structure of C60 fullerite in its low-temperature phase. It is shown that hexagons representing fullerenes oriented along the C3 axes of the sc lattice can be ordered into an ideal structure with four nonequivalent molecules in the unit cell. Then the energy degeneracy for the rotation of each hexagon by π/3 around its C3 axis leaves the translational and orientational order in this structure but leads to a random distribution of π/3 rotations and hence to an “averaged” unit cell with two molecules. However, the most relevant structural defects are not these intrinsic “misorientations” but some walls between domains with different sequences of the above-mentioned two (nonideal) sublattices. Numerical estimates are made for the anisotropic intermolecular potential, showing that the anisotropy is noticeably smaller for molecules in walls than in domains.
Characteristics of polarization switching from the low to the high frequency mode in vertical-cavity surface-emitting lasers
Authors: Ackemann T. , Sondermann M.
Published: July 2002

Polarization selection in small-area vertical-cavity surface-emitting lasers is studied experimentally in dependence of injection current and substrate temperature in the vicinity of the minimum threshold condition. Polarization switching from the low to the high frequency fundamental spatial mode is demonstrated. The effective birefringence displays a minimum in the transition region. The observation of dynamical transition states hints to the relevance of nonlinear effects. A comparison to the predictions of the San Miguel–Feng–Moloney model based on phase-amplitude coupling is given.
Optical heterodyne magnetic rotation enhanced velocity modulation spectroscopy: A sensitive absorption-based scheme for paramagnetic molecular ions
Authors: Luo Ming , Bi Zhiyi , Cai Peipei , Wang Rongjun , Yang Xiaohua , Chen Yangqin , Ma Longsheng
Published: July 2002

The sensitivity of velocity modulation spectroscopy (VMS) has been greatly improved by use of the frequency modulation enhanced magnetic rotation spectroscopic (FM-MRS) technique. This technique, which we refer to as optical heterodyne magnetic rotation enhanced VMS, has been described in detail in this article, including the experimental configuration, a discussion of line shape, and a systematic analysis of its sensitivity. N2+ has been used as a test sample of the technique, and the observed absorption spectrum of H2O+ in the visible region of 16 680–17 300 cm−1 further confirmed the significant improvement of the sensitivity by this VMS technique.
Counterion and polyion dynamics in highly asymmetrical electrolyte solutions
Authors: Jardat M. , Cartailler T. , Turq P.
Published: July 2002

Aqueous solutions of 1−10, 1−20, and 2−20 electrolytes with an asymmetry in size of 2:15 are studied for several volume fractions between 4% and 44%. The use of an efficient Brownian dynamics simulation method allows the investigation of the structural and dynamical properties of these systems. The pair interaction potential between ions is modeled by a pairwise soft-core repulsion (1/r9) and the Coulomb interaction. Self-diffusion coefficients of both polyions and counterions are calculated. The residence times of counterions in the vicinity of polyions are also computed. It is shown that a crystallization of macroions in a face centered cubic phase occurs for the 1−20 and 2−20 electrolytes at the highest concentration. In the 1−10 electrolyte at the same volume fraction, the macroions stay in a disordered structure. In any case the residence time of counterions around polyions is relatively small. Indeed, the self-diffusion of counterions is slightly increased in the 2−20 electrolyte when the electrolyte concentration is increased, whereas it is roughly constant in the other systems. Finally, the self-diffusion coefficients of polyions decrease strongly with regards to the infinite dilution, especially as they are charged.
The hyperfine structure in the electronic A 2E″←X 2E′ system of the pseudorotating lithium trimer
Authors: Meyer W. , Keil M. , Kudell A. , Baig M. A. , Zhu J. , Demtröder W.
Published: July 2002

Sub-Doppler laser spectroscopy of the A 2E″←X 2E′ band of Li3 shows well-resolved and characteristic hyperfine structures of rovibronic transitions which can be explained in all detail by the interplay between the underlying Fermi-contact interaction, the symmetry species of the rovibronic states and the Coriolis coupling of rotational and pseudorotational motions. Ab initio calculated electron spin densities reproduce the observed line splittings to within 3%. In this Jahn–Teller distorted molecule magnetic equivalence of identical nuclei is strictly valid only for rovibronic states of A symmetry. However, it also holds for rovibronic states of E symmetry if they are of pure A vibronic origin, and it is enforced for many E states of pure E vibronic origin by Coriolis coupling. In contrast, those transitions which involve states with dominant Kc=0 rotation functions and/or with strong vibronic E/A mixing show significant changes in the hyperfine patterns due to magnetic inequivalence, sometimes called “hyperfine doubling.”
Effective magnetostriction and magnetomechanical coupling of terfenol-D composites
Authors: Guo Z. J. , Busbridge S. C. , Piercy A. R. , Zhang Z. D. , Zhao X. G. , Wang B. W.
Published: July 2002

Epoxy and glass matrix Terfenol-D composites have been produced by using a cold and hot compression-molding technique, respectively. The static and dynamic magnetic and magnetomechanical properties of samples with a volume fraction Vf in the range of 10% to 82% have been investigated as functions of bias field, frequency, and ac drive field. The epoxy composites have a greater saturation magnetostrain than the glass composite with the same Vf. The elastic modulus of the epoxy composites is dominated by that of the matrix, Em. Increasing the value of Em reduces the measured magnetostriction λc of the composites. A model, based on the strain related energy equilibrium, has been developed to describe the experimental results for Vf and Em dependences of λc and the magnetomechanical coupling coefficient k33. It is concluded that an optimum k33 value can be obtained by choosing a matrix with an appropriate elastic modulus.
Rotating magnetohydrodynamic free-shear flows. I. Linear stability analysis
Authors: Yanase Shinichiro , Mizuguchi Masahiro , Riley James J.
Published: July 2002

The results of a study are presented of the linear stability of a magnetohydrodynamic planar free-shear flow subject to system rotation and a uniform magnetic field which are both parallel or antiparallel to the shear flow vorticity vector. The results show that, with anticyclonic rotation, the effect of the uniform magnetic field is to enlarge the unstable region of the rotating shear flow, while the growth rate of the most unstable disturbance is left unchanged. With cyclonic rotation, on the other hand, the effect of the magnetic field is to strongly stabilize the flow. The spatial structure of the anticyclonic magnetic shear/Coriolis instability mode is investigated. Considering the Rossby number at which the spatial extent of the most unstable disturbance becomes minimum, it is found that this Rossby number decreases as the uniform magnetic field is intensified.
Well-thickness dependence of emission from GaN/AlGaN separate confinement heterostructures
Authors: Gainer G. H. , Kwon Y. H. , Lam J. B. , Bidnyk S. , Kalashyan A. , Song J. J. , Choi S. C. , Yang G. M.
Published: July 2002

We investigated the effects of well thickness on spontaneous and stimulated emission (SE) in GaN/AlGaN separate confinement heterostructures (SCHs), grown by low-pressure metalorganic chemical vapor deposition. The SCH wells are unstrained and lattice-matched to a GaN buffer layer. Our series of SCHs had GaN well thicknesses of 3, 5, 9, and 15 nm. We explain the spontaneous emission peak energy positions of the SCHs in terms of spontaneous and strain-induced piezoelectric polarizations. At 10 K, the carrier lifetime was found to be lowest for a 3 nm well, and the SE threshold was lowest for a 5 nm well. We show that the screening of the piezoelectric field and the electron-hole separation are strongly dependent on the well thickness and have a profound effect on the optical properties of the GaN/AlGaN SCHs. The implications of this study on the development of near- and deep-ultraviolet light emitters are discussed.
Molecular dynamics studies on local ordering in amorphous polyethylene
Authors: Koyama Akira , Yamamoto Takashi , Fukao Koji , Miyamoto Yoshihisa
Published: July 2002

A molecular dynamics (MD) simulation was performed on a linear poly(ethylene) model under bulk amorphous conditions. A molecule was composed of united atoms (CH2 and CH3 unit), and the pressure of the MD cell was controlled to be 1 atm. The system was stepwise cooled from 600 to 120 K. At each temperature 2 ns simulation was performed. Local structural ordering proceeded as the temperature was lowered. The mean length of the trans sequences increased with decreasing temperature according to the Arrhenius law above 300 K. The correlation volume abruptly increased between 300 and 330 K, which is the measure of parallel ordered structure of the model chain used by Rigby and Roe. Fluctuations of the density, the length of the trans sequences, and the correlation volume developed toward the maximum values between 300 and 330 K. Then the fluctuations decreased with further cooling and the glass transition occurred at 230 K (≡Tg). A cluster was observed below Tg, which consisted of many planar-zigzag segments oriented in the same direction.
Microstructure and initial growth characteristics of the low temperature microcrystalline silicon films on silicon nitride surface
Authors: Park Young-Bae , Rhee Shi-Woo
Published: July 2002

Microstructure and initial growth characteristics of the hydrogenated microcrystalline Si (μc-Si:H) films grown on hydrogenated amorphous silicon nitride (a-SiNx:H) surface at low temperature were investigated using high resolution transmission electron microscope and micro-Raman spectroscopy. With increasing the Si and Si–H contents in the SiNx:H surfaces, μc-Si crystallites, a few nanometers in size, were directly grown on amorphous nitride surfaces. It is believed that the crystallites were grown through the nucleation and phase transition from amorphous to crystal in a hydrogen-rich ambient of gas phase and growing surface. The crystallite growth characteristics on the dielectric surface were dependent on the stoichiometric (x=N/Si) ratio corresponding hydrogen bond configuration of the SiNx:H surface. Surface facetting and anisotropic growth of the Si crystallites resulted from the different growth rate on the different lattice planes of Si. No twins and stacking faults were observed in the (111) lattice planes of the Si crystallites surrounding the a-Si matrix. This atomic-scale structure was considered to be the characteristic of the low temperature crystallization of the μc-Si:H by the strain relaxation of crystallites in the a-Si:H matrix.
Catalytic role of Au in Ni/Au contact on GaN(0001)
Authors: Kim C. C. , Kim J. K. , Lee J.-L. , Je J. H. , Yi M. S. , Noh D. Y. , Hwu Y. , Ruterana P.
Published: July 2002

We investigated the structural behavior of the Ni/Au contact on GaN(0001) and found the catalytic role of Au during annealing, using in situ x-ray scattering. The oxidation kinetics of Ni during annealing in air was greatly affected by the presence of Au. The accelerated GaN decomposition and Ni nitride formation during annealing in N2 also provide evidence of the catalytic role of Au. The results suggest that oxidized Ni/Au ohmic contact exhibit better thermal stability than that of the N2 annealed Ni/Au contacts.
Physical model for the evaluation of solid–liquid interfacial tension in silicon
Authors: Ujihara Toru , Sazaki Gen , Fujiwara Kozo , Usami Noritaka , Nakajima Kazuo
Published: July 2002

We proposed a simple lattice model to describe a solid–liquid interface of silicon based on experimental facts and molecular dynamics simulation results, and evaluated the relationship between the interface structure and the interfacial tension by comparing the model with experimental values. As a result, the entropy was found to give a major contribution to the interfacial tension, and it was revealed that the difference of entropy due to lattice disorder of bulk liquid and interface structure is the dominant factor of the entropy contribution. Moreover, the solid–liquid bond energy, which is crucial to estimate the contribution of the enthalpy, was successfully derived. The present model can be also applied to be the semiconductor material which has a diamond structure or a zinc blende structure.
Statistical analysis of multiple cracking phenomenon of a SiOx thin film on a polymer substrate
Authors: Yanaka M. , Tsukahara Y. , Okabe T. , Takeda N.
Published: July 2002

The progress of multiple cracking in a silicon oxide (SiOx) film deposited onto a polyethylene terephthalate substrate was analyzed using Monte Carlo simulation. The finite-element analysis, assuming elastoplastic behavior of the polymer substrate, was conducted to calculate the stress distributions in film fragments and was used in the simulation. The Weibull parameters of the film were determined from the scatter of crack onset strain. The simulation predicted successfully the crack density and the distribution of fragment lengths during the progress of multiple cracking. The validity of the shear lag analysis based on the unique stress criterion in a previous study was also evaluated.
Interface engineering of a ZrO2/SiO2/Si layered structure by in situ reoxidation and its oxygen-pressure-dependent thermal stability
Authors: Watanabe Heiji
Published: July 2002

Reactions at ZrO2/SiO2/Si interfaces during fabrication and postannealing have been studied in detail. The layered structures were fabricated by deposition of a thin Zr layer on a chemical oxide, followed by oxidation in an UHV chamber without air exposure (i.e., in situ reoxidation). On-line x-ray photoelectron spectroscopy was used to show that in situ reoxidation can be used for precisely designing interfacial structures. It was found that the thermal stability of ZrO2/SiO2/Si interfaces crucially depends on oxygen ambient; that is, while the interfaces are stable up to 900 °C under UHV conditions, annealing in 1×10−4 Torr oxygen results in formation of interfacial Zr silicate. Moreover, the ZrO2 overlayer was found to accelerate the interfacial oxidation reaction.
Formation and destruction of cube texture in MgO films using ion beam assisted pulsed laser deposition
Authors: Hühne Ruben , Beyer Christoph , Holzapfel Bernhard , Oertel Carl-Georg , Schultz Ludwig , Skrotzki Werner
Published: July 2002

Biaxially textured MgO thin films were deposited on amorphous substrates using ion beam assisted pulsed laser deposition. The development of the texture and microstructure was investigated with electron diffraction and atomic force microscopy. After the first few nanometers of growth, a sharp nucleation texture is observed. During further growth a texture change takes place, leading to two texture components, one in the 〈220〉 direction and the other in the 〈111〉 direction parallel to the substrate normal. In both cases the 〈200〉 direction is parallel to the ion beam. This texture change can be explained in terms of the highly anisotropic sputter rate observed in experiments on single crystals, leading to grains having a 〈200〉 direction parallel to the ion beam during growth being preferred. Without ion beam assistance during further growth, one of the two texture components dominates.
Theoretical study of the photochemistry of Cl2O
Authors: Collaveri C. , Granucci G. , Persico M. , Toniolo A.
Published: July 2002

This is a theoretical study of the photochemistry of Cl2O based on ab initio potential energy surfaces and trajectory surface-hopping calculations. We calculated quasidiabatic states and couplings for eight singlet states of Cl2O with a multireference perturbation configuration interaction (CI) technique. Analytical representations of the three-dimensional potential energy surfaces and electronic couplings were used for semiclassical simulations of the nonadiabatic dynamics of excited Cl2O up to 5.4 eV. The computational results allow us to relate the photodissociation mechanism to observable quantities such as the anisotropy of the recoil velocity and the translational energy distribution of the fragments.
Thermodynamics and kinetics of folding of a small peptide
Authors: Hansmann Ulrich H. E. , Onuchic Jose N.
Published: July 2002

We study the thermodynamics and kinetics of folding for a small peptide. Our data rely on Monte Carlo simulations where the interactions among all atoms are taken into account. Monte Carlo kinetics is used to study folding of the peptide at suitable temperatures. The results of these canonical simulations are compared with that of a generalized-ensemble simulation. Our work demonstrates that concepts of folding which were developed in the past for minimalist models hold also for this peptide when simulated with an all-atom force field.
Instantaneous optical modulation in bulk GaAs semiconductor microcavities
Authors: Sanchez S. , De Matos C. , Pugnet M.
Published: July 2002

Picosecond pump–probe experiments at room temperature on a bulk GaAs microcavity are presented. The microcavity device is designed to adjust the cavity mode energy 15 meV below the band gap energy of the intracavity bulk GaAs material. For low pump-energy densities (∼μJ/cm2), ultrafast modulation of the reflectivity is demonstrated due to the purely coherent refractive index change. A 5:1 contrast ratio is achieved and shows the potential of the semiconductor microcavities for implementation in ultrafast all optical switching.
Determination of the radial density distribution of ground and low-lying levels of mercury in a nonequilibrium plasma using emission spectroscopy
Authors: Karabourniotis Dimitrios
Published: July 2002

A method is described for determining the radial density distribution of the ground and the first excited states as well as the electron temperature distribution in multielement plasmas containing mercury. It is based on the spectroscopic measurement of the plasma emissivity at the maximum of self-reversed lines and the population density of a high-lying excited state. The method is independent of equilibrium assumptions and can be used in diagnostics of nonequilibrium plasmas. The proposed method was verified for the plasma of a 5 bar discharge in mercury. Plasma underionization and nonequilibrium excitation are observed spectroscopically in the bulk of the discharge. The experimental data are interpreted in terms of nonequilibrium effects. Comparison of the results obtained initially, and then assuming local thermodynamic equilibrium (LTE), shows clearly considerable departure of the plasma from LTE.
The lowest doublet and quartet potential energy surfaces involved in the N(4S)+O2 reaction. I. Ab initio study of the Cs-symmetry (2A′, 4A′) abstraction and insertion mechanisms
Authors: Sayós R. , Oliva Carolina , González Miguel
Published: July 2002

In this work we have carried out ab initio complete active space self-consistent-field (CASSCF) calculations, second-order perturbation calculations based on CASSCF wave functions (CASPT2), uncontracted multireference configuration interaction calculations, and some density functional calculations with standard correlation-consistent Dunning basis sets and atomic natural orbital basis sets on the lowest A′2 and A′4 potential energy surfaces involved in the title reaction. The ground A′2 surface has an average energy barrier of 5.3 kcal/mol in the CASPT2 complete basis set limit. A peroxy NOO minimum is found in agreement with preceding ab initio works, which seems to play an important role in the opening of a double microscopic mechanism: direct Cs abstraction and indirect Cs insertion through the NO2(X 2A1) molecule. The ground A′4 surface shows an average energy barrier of 13.5 kcal/mol in the CASPT2 complete basis set limit. Despite this excited surface displays another peroxy minimum, in this case only a direct Cs-abstraction mechanism can be expected. The present results improve previous high quality ab initio studies and provide lower energy barriers in both potential energy surfaces, which would produce larger total thermal rate constants in better agreement with experimental data. Finally, it is demonstrated that the N and O 2s electron correlation cannot be neglected as it produces a significant decrease in both energy barriers.
Anisotropic diffusion and drift of photogenerated carriers near coreless dislocations in InGaN quantum well
Authors: Shi L. , Poweleit C. D. , Ponce F. A. , Menendez J. , Chow W. W.
Published: July 2002

We report on a photoluminescence (PL) study on pinholes and their effects on the carrier recombination process in an InGaN/GaN single quantum well sample. By directly imaging the luminescence from the sample, we observed an anisotropic distribution of photogenerated carriers due to diffusion and drift of the carriers near pinholes. The anisotropy, together with micro-PL spectra at different locations near a pinhole, shows evidence of narrowing of the band gap of the quantum well layer near pinholes. The existence of the band gap gradient is confirmed by reflective and photoluminescence images of the sample under global illumination. Possible causes of the band gap gradient include indium concentration inhomogeneity and partial strain relaxation near pinholes.
Variable-wavelength switchable Bragg gratings formed in polymer-dispersed liquid crystals
Authors: Bowley Chris C. , Kossyrev Pavel A. , Crawford Gregory P. , Faris Sadeg
Published: July 2002

We report a holographic polymer-dispersed liquid crystal cell whose reflection peak can be tuned as a function of applied voltage. Electro-optic results are presented which are in excellent agreement with our model based on coupled wave theory.
Eddies induced in cylindrical containers by a rotating end wall
Authors: Hills Christopher P.
Published: July 2002

The flow generated in a viscous liquid contained in a cylindrical geometry by a rotating end wall is considered. Recent numerical and experimental work has established several distinct phases of the motion when fluid inertia plays a significant role. The current paper, however, establishes the nature of the flow in the thus far neglected low Reynolds number regime. Explicitly, by employing biorthogonality relations appropriate to the current geometry, it is shown that a sequence of exponentially decaying eddies extends outward from the rotating end wall. The cellular structure is a manifestation of the dominance of complex eigensolutions to the homogeneous problem and arises as the result of nonlinear forcing associated with an inertial correction to the Stokes flow.
A calculation model for density limits in auxiliary heated, gas fueled tokamaks and application to DIII-D model problems
Authors: Stacey Weston M.
Published: July 2002

A model for the calculation of density limits in high confinement (H-mode) tokamaks is described. The model consists of coupled calculations of (1) the power, particle and momentum balances for the core plasma and for the divertor/SOL (scrape-off layer) plasma; (2) the transport of fueling and recycling neutrals; (3) pedestal gradient scale lengths and MHD (magnetohydrodynamic) limits; (4) confinement degradation due to thermal instabilities in the edge transport barrier; (5) divertor and core MARFE (multifaceted asymmetric radiation from edge) onset; (6) radiative collapse leading to disruption, and (7) power threshold for high-to-low mode transition. The model is applied to study the effects of different operational parameters (e.g., P, I, B) on the density limit for auxiliary heated, gas fueled DIII-D [J. L. Luxon, F. Batty, C. B. Baxi et al., Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] model problems. Predicted values of densities, temperatures, and edge gradient scale length are generally consistent with measured values, and many of the phenomena observed experimentally in association with density limits are predicted. It is found that the MARFE density limit increases strongly with increasing auxiliary heating power per unit plasma surface area (i.e., power flux exiting the core into the SOL) and with increasing plasma current, and decreases weakly with increasing magnetic field and with increasing carbon impurity concentration.
Structure and electrical properties of Pb(ZrxTi1−x)O3 deposited on textured Pt thin films
Authors: Hong Jongin , Song Han Wook , Lee Hee Chul , Lee Won Jong , No Kwangsoo
Published: July 2002

The texturing of the bottom electrode plays a key role in the structure and electrical properties of Pb(Zr, Ti)O3 (PZT) thin films. We fabricated Pt bottom electrodes having a different thickness on MgO single crystals at 600 °C by rf magnetron sputtering. As the thickness of platinum (Pt) thin film increased, the preferred orientation of Pt thin film changed from (200) to (111). PZT thin films were fabricated at 450 °C by electron cyclotron resonance-plasma enhanced metal organic chemical vapor deposition on the textured Pt thin films. The texturing of the bottom electrode caused drastic changes in the C–V characteristics, P–E characteristics, and fatigue characteristics of metal/ferroelectric material/metal (MFM) capacitors. The difference of the electrical properties between the PZT thin films having different texturing was discussed in terms-of the x–y alignment and the interface between electrode and PZT in MFM capacitors.