bluuebunny/crossref_metadata_2025 huggingface dataset:
A review of symbolic analysis of experimental data
Authors: Daw C. S. , Finney C. E. A. , Tracy E. R.
Published: January 2003

This review covers the group of data-analysis techniques collectively referred to as symbolization or symbolic time-series analysis. Symbolization involves transformation of raw time-series measurements (i.e., experimental signals) into a series of discretized symbols that are processed to extract information about the generating process. In many cases, the degree of discretization can be quite severe, even to the point of converting the original data to single-bit values. Current approaches for constructing symbols and detecting the information they contain are summarized. Novel approaches for characterizing and recognizing temporal patterns can be important for many types of experimental systems, but this is especially true for processes that are nonlinear and possibly chaotic. Recent experience indicates that symbolization can increase the efficiency of finding and quantifying information from such systems, reduce sensitivity to measurement noise, and discriminate both specific and general classes of proposed models. Examples of the successful application of symbolization to experimental data are included. Key theoretical issues and limitations of the method are also discussed.
Multiple sample manipulator with five degrees of freedom for angle-resolved spectroscopy in ultrahigh vacuum
Authors: Finstad C. C. , Schabel M. J. , Muscat A. J.
Published: January 2003

A Physical Electronics ultrahigh vacuum bell jar was retrofitted with a customized sample manipulator to add angle resolved x-ray photoelectron spectroscopy (ARXPS) and Auger electron spectroscopy capabilities. The custom manipulator accommodates up to four commercial sample holders on vertical forks in a carousel arrangement, with each sample facing radially outward. The forks are mounted on support levers. Concentric shafts depress the inner edge of the support levers to tilt the samples without gearing. The design permits tilt angles between 0 and 75°, though angles greater than 35° are impractical with a cylindrical mirror analyzer (CMA). The manipulator does not facilitate azimuthal rotation, requiring samples to be reloaded for each desired orientation change. The performance of the manipulator was characterized using ARXPS measurements of a native silicon dioxide film on silicon. A film thickness of approximately 4.7 Å, between one and two layers thick, was obtained from a model fit to the data using the relative ratio method adapted for a CMA not equipped with an angle-selecting aperture.
DoseSim: Microsoft-Windows graphical user interface for using synchrotron x-ray exposure and subsequent development in the LIGA process
Authors: Meyer P. , Schulz J. , Hahn L.
Published: January 2003

The LIGA process, which combines x-ray lithography with electroplating and moulding, is a technique used worldwide for the fabrication of high aspect ratio microstructures. In the first step (x-ray lithography), a resist layer is applied to a metal-coated substrate, which is then patterned by shadow printing through an x-ray mask with synchrotron radiation. The second step consists in dissolving the exposed parts or the unexposed parts, of a positive and negative resist, respectively, in an organic developer. A graphical user interface has been developed, working under Windows, which meets the necessary requirements of a LIGA x-ray beamline. The code currently permits the computation of synchrotron radiation from bending magnets, the effects of the optical properties of materials, and the necessary parameters for the resist exposure. Also, this program is highly flexible and allows the user to access many annexed calculation possibilities, for example, optimization of the absorber thickness for a desired dose after the absorber, filter possibilities for a desired ratio top dose/bottom dose, calculation of the necessary time to develop the exposed resist. The comparison of results of this code and data used by different x-ray LIGA centers will be given. A general overview of the possibilities of this program will be presented.
Proof-of-principle laser-induced fluorescence measurements of gas distributions from supersonic nozzles
Authors: Failor B. H. , Chantrenne S. , Coleman P. L. , Levine J. S. , Song Y. , Sze H. M.
Published: January 2003

We have applied the technique of acetone laser-induced fluorescence (LIF) to the measurement of gas distributions from axisymmetric supersonic nozzles used to produce loads for z-pinch plasma radiation sources. Typical peak particle densities are ∼1017 particles/cm3 for loads imploded on the Double-EAGLE facility. The experimental approach uses a pulsed laser (266 nm wavelength, 2.2 mJ per pulse, 5 ns pulse width, and 3×107 W/cm2 intensity) to obtain a snapshot along a chord through the center of the gas density distribution at an arbitrary axial distance, z, from the nozzle exit. We report measurements at 4.3 and 20.0 mm from the exit of the nozzle for comparison with previous measurements. We find acceptable agreement between LIF and laser interferometer measurements. Strengths of the LIF approach include simplicity of implementation and high radial spatial resolution.
Characteristics of an E×B probe for extraction of H− ions from a magnetized sheet plasma source
Authors: Arciaga Marko E. , Mendenilla Alexander G. , Ramos Henry J.
Published: January 2003

An E×B probe is characterized by investigating its two parameters, namely extraction voltage (Vext) and lens voltage (Vlens). The effects of Vext and Vlens on the extracted H− ion current are examined. The investigation of Vext effects is done with a constant Vlens=0 V. The results show that the optimum value for negative ion extraction is Vext=190 V. With this optimum Vext, the Vlens parameter is examined. Findings show that the optimum Vlens is 0 V. Optimized parameters give the highest ion current and narrowest full width at half maximum. With these optimum settings, the E×B probe is used to study the variation of H− ions as a function of perpendicular distance (i.e., 1 cm to 4 cm) from the center of a magnetized sheet plasma with Bave=6.59 mT.
Inhomogeneous gas model for electron mobility in high density neon gas
Authors: Borghesani A. F. , O’Malley T. F.
Published: January 2003

Experimental studies of electron mobilities in Neon as a function of the gas density up to moderately high densities have persistently shown mobilities up to an order of magnitude smaller than expected and predicted. A previously ignored mechanism (gas in-homogeneity which is negligible in the thermal mobilities for He and other gases) is found to reproduce the observed Neon mobilities accurately and simply at five temperatures with just the density deficit as the single variable parameter. Recognizing that a gas is not a homogeneous medium, a variation in local density, combined with the quantum multiscattering theory, shifts the energy and cross section—which in turn changes the collision probability and finally the mobilities. A lower density where a momentum transfer interaction occurs moves the mobility strongly in the same direction as the anomalous results of the experiments. By going backwards from the observed mobilities, the collision frequency at each temperature and density is made to reproduce the experimental data by looking for the local (as opposed to average) density at which the (rare) momentum transfer interactions occur. These density deviations give a picture of the size and behavior of the wave packets for electron motion which looks very much like the often discussed wave function collapse.
Dynamical ionization of the 4He trimer: A time-dependent modeling of its fragmentation
Authors: Satta M. , Scifoni E. , Gianturco F. A.
Published: January 2003

4 He trimer 3D-photoionization has been studied using a new quantum time-dependent model based on a wavelet expansion of the time-dependent vibrational self-consistent-field equations. Dissociation probabilities and final vibrational populations of the fragment molecules, together with time-snapshots of the angular distributions during fragmentation, are analyzed. Special emphasis is given to the internal vibrational rearrangements occurring during the fragmentation process following the photoionization event. Our calculations found (He2+)* to be preferentially formed in one of its vibrationally excited states and also that the amount of (He3+)* surviving the fragmentation, is mostly left in vibrationally excited states involving its ionic part.
Integral and differential cross section measurements at low collision energies for the N2++CH4/CD4 reactions
Authors: Nicolas Christophe , Torrents Raquel , Gerlich Dieter
Published: January 2003

Absolute integral cross sections are measured in the collision energy range between 0.1 to 3.5 eV for the N2++CH4 and N2++CD4 reactions using the universal guided ion beam apparatus. The reaction branching ratio, CX3+:CX2+:N2X+ (X=H or D), is found to be 0.86:0.09:0.05 and 0.88:0.07:0.05 for the N2++CH4 and N2++CD4 reactions, respectively. The CH3+/CH2+ ratio is constant over the whole collision energy range and very similar to the one obtained for the almost isoenergetic Ar++CH4 reaction. Axial velocity distributions of the product ions are measured by time of flight at collision energies between 0.1 and 3.5 eV. The results provide direct insight into the reaction dynamics. The dissociative charge transfer channels, leading to CH3+ and CH2+ product ions, occur via an electron jump combined with some exchange of momentum between the colliding partners. The H (D) transfer leading to N2H+ can be described as a direct process, similar to a spectator stripping mechanism. Various isotope effects are observed, the dominant being that the cross sections for reaction with CH4 are up to 20% bigger than the corresponding ones for CD4.
Structural and spectroscopic trends in the ground states of the monohalosilylenes: Emission spectroscopy of jet-cooled HSiI and DSiI
Authors: Tackett Brandon S. , Clouthier Dennis J.
Published: January 2003

Single vibronic level emission spectra of jet-cooled HSiI and DSiI have been recorded by laser excitation of selected bands of the Ã1A″–X̃1A′ electronic transition. The data have been used to derive the ground state harmonic frequencies and anharmonicities for both isotopomers. A normal coordinate analysis of the harmonic frequencies yielded reliable values for five of the six force constants. Using previously determined ground state rotational constants and the force field data, average (rz) and approximate equilibrium (rez) structures were calculated, with rez(SiH)=1.5151(2) Å, rez(SiI)=2.4610(1) Å, and θez(HSiI)=92.5(1)°. A comparison of trends in the structural parameters and vibrational frequencies of the monohalosilylenes shows that the bond angle increases significantly and the Si–H bond length decreases slightly with heavier halogen substitution. These trends have been rationalized based on the inductive effect and the electronegativity of the halogen substituent.
Accurate electric multipole moment, static polarizability and hyperpolarizability derivatives for N2
Authors: Maroulis George
Published: January 2003

We report accurate values of the electric moments, static polarizabilities, hyperpolarizabilities and their respective derivatives for N2. Our values have been extracted from finite-field Møller–Pleset perturbation theory and coupled cluster calculations performed with carefully designed basis sets. A large [15s12p9d7f] basis set consisting of 290 CGTF is expected to provide reference self-consistent-field values of near-Hartree–Fock quality for all properties. The Hartree–Fock limit for the mean hyperpolarizability is estimated at γ̄=715±4e4a04Eh−3 at the experimental bond length Re=2.074 32a0. Accurate estimates of the electron correlation effects were obtained with a [10s7p6d4f] basis set. Our best values are Θ=−1.1258ea02 for the quadrupole and Φ=−6.75ea04 for the hexadecapole moment, ᾱ=11.7709 and Δα=4.6074e2a02Eh−1 for the mean and the anisotropy of the dipole polarizability, C̄=41.63e2a04Eh−1 for the mean quadrupole polarizability and γ̄=927e4a04Eh−3 for the dipole hyperpolarizability. The latter value is quite close to Shelton’s experimental estimate of 917±5e4a04Eh−3 [D. P. Shelton, Phys. Rev. A 42, 2578 (1990)]. The R dependence of all properties has been calculated with a [7s5p4d2f] basis set. At the CCSD(T) level of theory the dipole polarizability varies around Re as ᾱ(R)/e2a02Eh−1=11.8483+6.1758(R−Re)+0.9191(R−Re)2−0.8212(R−Re)3−0.0006(R−Re)4, Δα(R)/e2a02Eh−1=4.6032+7.0301(R−Re)+1.9340(R−Re)2−0.5708(R−Re)3+0.1949(R−Re)4. For the Cartesian components and the mean of γαβγδ, (dγzzzz/dR)e=1398, (dγxxxx/dR)e=867, (dγxxzz/dR)e=317, and (dγ̄/dR)e=994e4a03Eh−3. For the quadrupole polarizability Cαβ,γδ, we report (dCzz,zz/dR)e=19.20, (dCxz,xz/dR)e=16.55, (dCxx,xx/dR)e=10.20, and (dC̄/dR)e=23.31e2a03Eh−1. At the MP2 level of theory the components of the dipole–octopole polarizability (Eα,βγδ) and the mean dipole–dipole–octopole hyperpolarizability B̄ we have obtained (dEz,zzz/dR)e=36.71, (dEx,xxx/dR)e=−12.94e2a03Eh−1, and (dB̄/dR)e=−108e3a03Eh−2. In comparison with some other 14-electron systems, N2 appears to be less (hyper)polarizable than most, as near the Hartree–Fock limit we observe ᾱ(N2)<ᾱ(CO)<ᾱ(HCN)<ᾱ(BF)<ᾱ(HCCH) and γ̄(N2)<γ̄(CO)<γ̄(HCN)<γ̄(HCCH)<γ̄(BF).
Dissociative electron attachment near threshold, thermal attachment rates, and vertical attachment energies of chloroalkanes
Authors: Gallup G. A. , Aflatooni K. , Burrow P. D.
Published: January 2003

The peaks appearing near zero energy in the dissociative electron attachment cross section of 18 chloroalkanes are studied by electron beam methods. Fits to the experimental data are made using model cross sections having appropriate energy dependences and inclusion of the broadening due to the electron energy distribution. The magnitudes of the zero peaks are found to be well correlated with the vertical attachment energies (VAE) associated with occupation of the lowest empty orbitals of the compounds. The magnitudes rise exponentially by more than five orders of magnitude as VAE decreases from 2 eV to a slightly negative value. This dependence is a consequence not only of the thermal population of vibrational levels, but also of an approximately linear relationship between VAE and the energy of the crossing between the neutral and anion potential curves. Franck–Condon factors for the transition to the anion curve are computed for model potential curves, and the nature of the attachment from vibrational levels with energies near that of the crossing point is explored in a local potential resonance picture. A substantial contribution arises from tunneling to the anion state from vibrational levels below the barrier. Thermal attachment rate constants are also computed from our data. These are also shown to vary exponentially with VAE.
Collective diffusion and self-diffusion coefficients comparison to separate interactions and micellar size effects on ionic micelle diffusivities: Cylindrical micelles of sodium taurodeoxycholate
Authors: Galantini Luciano , Pavel Nicolae Viorel
Published: January 2003

Collective and self-diffusion coefficients of sodium taurodeoxycholate (NaTDC) and taurocholate (NaTC) D2O micellar solutions were measured, as a function of ionic strength (0–0.6 M NaCl added) and bile salt concentration, by means of quasielastic light-scattering and 1H pulse-gradient-spin-echo nuclear magnetic resonance measurements. A data analysis, performed by using a simple model of monodisperse Brownian particles with hydrodynamic interaction and hard-core repulsion, allowed us to separate the effect of micellar size and particle interactions at low ionic strength. An estimation of the hydrodynamic radius and of the Debye–Hückel interaction strength was obtained without extrapolating the data to the critical micellar concentration. A discussion based on a hard-body interacting cylinder model suggests that attractive interactions influence the NaTDC diffusivities at high NaCl concentration. With respect to NaTC, at the same ionic strength, greater effective charge and size characterize the NaTDC micellar aggregates that, moreover, show a more extended growth as a function of NaCl and bile salt concentration.
The stability of planar Couette flow simulated by molecular dynamics
Authors: McWhirter J. Liam
Published: January 2003

We review the linear stability analysis of the Navier–Stokes (NS) equation, and consider the Loose–Hess stability analysis of simulated atomic and molecular fluids under planar Couette flow. Traditional linear stability analysis of the NS equation fails to predict the critical Reynolds number where steady-state fluid flow becomes unstable. This failure arises because this analysis only treats perturbations to the steady-state flow which are single-eigenmode solutions of the linearized NS equation. By contrast, modern stability analysis of the NS equation, that considers perturbations which are superpositions of such modes, predicts that planar Couette flow can become unstable at Reynolds numbers less than that predicted by the traditional analysis. We show that the Loose–Hess stability theory, whose derivation resembles the traditional analysis of the NS equation, can accurately predict the critical shear rates where the flows of Lennard-Jones and simple dipolar fluids cease to be stable. Furthermore, noting the predictions made by the stability analyses of the NS equation, we describe the global stability of planar Couette flow simulated by molecular dynamics.
Folding transition of model protein chains characterized by partition function zeros
Authors: Wang Jun , Wang Wei
Published: January 2003

The folding transition of model protein chains with various kinds of Gō-type interactions are investigated by partition function zeros on complex temperature plane. Using multicanonical sampling procedures, the density of states and thus the partition function zeros are precisely obtained. Several factors related to the local distribution of the partition function zeros near the real axis are extracted and used to characterize the features of folding transition. The results show that the folding transition is of first-order-like, and is weakly dependent on the native structures. The efficiency of the method of partition function zero is also illustrated. The correlation between some conventional thermodynamic factors for characterizing the stability and foldability and those obtained from the zeros are also studied. Finally, a mapping between the various models and the Gō-type models is proposed based on the factors related to zeros, which suggests the wide applicability of the method based on the partition function zeros.
Hydration free energy and potential of mean force for a model of the sodium chloride ion pair in supercritical water with ab initio solute–solvent interactions
Authors: Liu Wenbin , Wood Robert H. , Doren Douglas J.
Published: January 2003

The free energy of hydration, ΔhG, and the potential of mean force (PMF) of a quantum-mechanical (QM)–molecular mechanical (MM) model of the NaCl ion pair at 973 K with 0.535 g/cm3 has been calculated using the ab initio/classical free-energy perturbation (ABC-FEP) method proposed by Wood et al. [J. Chem. Phys. 110, 1329 (1999)]. This method allows calculation of ΔhG and the PMF of a QM-MM model in which Na+-Cl−, Na+-H2O, and Cl−-H2O interactions are calculated by ab initio QM methods and only the H2O-H2O interactions are calculated by a MM model [Rick, Stuart, and Berne, J. Chem. Phys. 101, 6141 (1994)]. The only simulations required are of an approximate MM model. The free energy of the QM-MM model is obtained from a relatively small number of QM energy calculations via free-energy perturbation theory. These QM energies are obtained by calculating pair-wise interactions at the second-order Møller–Plesset/ 6-311++G(3df,3pd) level, and multibody interactions at the B3LYP/ 6-311++G(3df,3pd) level. The PMF predicts an association constant, log Kc=2.3±0.3, for the NaCl ion pair. This compares favorably with the experimental value of Quist and Marshall [J. Phys. Chem. 72, 684 (1968)], log Kc=2.6 (interpolated at 0.535 g/cm3) and demonstrates the ability of the ABC-FEP method to predict the PMF and the association constant of an ion pair. There are important contributions to the PMF from non-pairwise-additive contributions to the Na+-Cl− interaction. While previous calculations have accounted for these non-pairwise-additive contributions through effective pairwise-additive models, the ABC-FEP method includes them exactly, within the accuracy of an ab initio calculation.
Critical behavior of a ternary ionic system: A controversy
Authors: Gutkowski Karin I. , Bianchi Hugo L. , Japas M. Laura
Published: January 2003

Refractive indices n of coexisting phases and turbidity τ of an homogeneous sample of the ternary system water+3-methyl pyridine +sodium bromide were measured near its lower consolute point. In both cases, the global composition of the samples was fixed (0.170 mass fraction of sodium bromide, 0.599 mass fraction of water). The system was previously reported to exhibit a tremendous change in the critical exponent γ as the salt concentration increased from 0.08 to 0.17 mass fraction. Data also recorded a marked increase in the background turbidity, and the system was therefore suspected of displaying multicritical behavior. Refractive index measurements were carried out in the reduced temperature range 1×10−4⩽t=(T−Tc)/Tc⩽0.02. Turbidity data were obtained for 6×10−4⩽t⩽0.032. In addition, electrical conductivities of the solution were measured as a function of the concentration of salt, in the homogeneous region along an isothermal (298.12 K) path of fixed 3-methyl pyridine/water ratio. Although critical coordinates of our sample agree with those previously reported, we were unable to see any trace of multicritical behavior.
Lasing properties of GaAs/(Al,Ga)As quantum-cascade lasers as a function of injector doping density
Authors: Giehler M. , Hey R. , Kostial H. , Cronenberg S. , Ohtsuka T. , Schrottke L. , Grahn H. T.
Published: January 2003

The lasing properties of GaAs/Al0.33Ga0.67As quantum-cascade lasers are investigated as a function of injector doping concentration ns between 2×1011 and 1×1012 cm−2 per period. Lasing is observed for ns⩾3.5×1011 cm−2, with optimal lasing properties (minimum of the threshold current and maximum of the modified characteristic temperature) for nopt≈6×1011 cm−2. With increasing ns up to nopt, the lasing energy of 115 meV exhibits first a blueshift to 135 meV, followed by a redshift to 120 meV for higher doping levels. This shift of the lasing energy as a function of ns is discussed in terms of changes in the field distribution, occupation of additional levels above the upper laser level, and electron–electron interactions.
Nanoscale organic transistors that use source/drain electrodes supported by high resolution rubber stamps
Authors: Zaumseil Jana , Someya Takao , Bao Zhenan , Loo Yueh-Lin , Cirelli Raymond , Rogers John A.
Published: January 2003

Soft contact lamination and metal-coated elastomeric stamps provide the basis for a convenient and noninvasive approach to establishing high resolution electrical contacts to electroactive organic materials. The features of relief on the stamps define, with nanometer resolution, the geometry and separation of electrically independent electrodes that are formed by uniform, blanket evaporation of a thin metal film onto the stamp. Placing this coated stamp on a flat substrate leads to “wetting” and atomic scale contact that establishes efficient electrical connections. When the substrate supports an organic semiconductor, a gate dielectric and a gate, this soft lamination process yields high performance top contact transistors with source/drain electrodes on the stamp. We use this approach to investigate charge transport through pentacene in transistor structures with channel lengths that span more than three decades: from 250 μm to ∼150 nm. We also report some preliminary measurements on charge transport through organic monolayers using the same laminated transistor structures.
Electronic and magnetic properties of MnN versus MnAs
Authors: Janotti A. , Wei Su-Huai , Bellaiche Laurent
Published: January 2003

Electronic and magnetic properties of MnN and MnAs compounds in the hypothetical cubic zinc-blende phase are studied using first-principles band structure method. We show that the high electronegativity and small atomic size of N compared to As lead to interesting consequences: MnN has a low-spin antiferromagnetic ground state, whereas MnAs has a high-spin hole mediated ferromagnetic (FM) ground state. Because the Mn d bands are higher in energy than the N p band, Mn is not efficient to generate free holes in the nitrides. Therefore, previous prediction that undoped Ga1−xMnxN diluted alloy can result in room-temperature FM semiconductor should be reexamined.
Flux pinning enhancement in ferromagnetic and superconducting thin-film multilayers
Authors: Jan D. B. , Coulter J. Y. , Hawley M. E. , Bulaevskii L. N. , Maley M. P. , Jia Q. X. , Maranville B. B. , Hellman F. , Pan X. Q.
Published: January 2003

Flux pinning in high-temperature superconductors such as YBa2Cu3O7−x (YBCO) in the past has been accomplished by pinning the vortex cores. We demonstrate magnetic-domain-induced flux pinning of the magnetic flux of vortices in a ferromagnet-superconductor bilayer consisting of CoPt grown on YBCO, where the ferromagnet has uniaxial perpendicular magnetic anisotropy and a random domain structure. We observe an improvement of the critical current due to magnetic pinning at temperatures close to the transition temperature.
ZnO-based transparent thin-film transistors
Authors: Hoffman R. L. , Norris B. J. , Wager J. F.
Published: January 2003

Highly transparent ZnO-based thin-film transistors (TFTs) are fabricated with optical transmission (including substrate) of ∼75% in the visible portion of the electromagnetic spectrum. Current–voltage measurements indicate n-channel, enhancement-mode TFT operation with excellent drain current saturation and a drain current on-to-off ratio of ∼107. Threshold voltages and channel mobilities of devices fabricated to date range from ∼10 to 20 V and ∼0.3 to 2.5 cm2/V s, respectively. Exposure to ambient light has little to no observable effect on the drain current. In contrast, exposure to intense ultraviolet radiation results in persistent photoconductivity, associated with the creation of electron-hole pairs by ultraviolet photons with energies greater than the ZnO band gap. Light sensitivity is reduced by decreasing the ZnO channel layer thickness. One attractive application for transparent TFTs involves their use as select-transistors in each pixel of an active-matrix liquid-crystal display.
Junction parameter control of Bi2Sr2CaCu2O8+δ stacked junctions by annealing
Authors: Inomata K. , Kawae T. , Nakajima K. , Kim S.-J. , Yamashita T.
Published: January 2003

The control of the critical current density (Jc) and the junction resistance (RN) along the c axis of intrinsic Josephson junctions (IJJs) on a high-Tc superconductor is very important for applying the IJJs to electronic devices. For controlling these junction parameters, we have clarified the relationship of Jc, RN, and the carrier density in Bi2Sr2CaCu2O8+δ (Bi-2212) whiskers by changing the carrier density with an annealing process. As a result, the Jc decreased, and the RN increased systematically when the carrier density decreased. The values of Jc and RN could be controlled by a change in the carrier density.
Lattice parameters of GaN layers grown on a-plane sapphire: Effect of in-plane strain anisotropy
Authors: Darakchieva V. , Paskov P. P. , Paskova T. , Valcheva E. , Monemar B. , Heuken M.
Published: January 2003

We have studied GaN films grown on a-plane sapphire by hydride vapor phase epitaxy and metalorganic vapor phase epitaxy. The in-plane lattice parameter was determined from sets of equivalent interplanar distances measured for six different directions in order to examine the effect of strain anisotropy. It is found that, in both types of films, the obtained six values of the in-plane lattice parameter can be grouped around two values. The strain anisotropy is estimated to have different value in the films grown by the two techniques and possible explanations are suggested.
Formation of shallow source/drain extensions for metal–oxide–semiconductor field-effect-transistors by antimony implantation
Authors: Rücker H. , Heinemann B. , Barth R. , Bolze D. , Melnik V. , Krüger D. , Kurps R.
Published: January 2003

Shallow Sb and As junctions have been investigated with regard to their applicability in complementary metal–oxide–semiconductor (CMOS) technologies. Replacing As source/drain extensions by Sb with the same implanted depth facilitates the formation of about 20 nm shallower junctions and even lower sheet resistance. This is due to the absence of transient enhanced diffusion effects and less dose loss for Sb. Sb source/drain extensions with a final junction depth of 40 nm and a sheet resistance of 320 Ω/sq have been integrated in a standard CMOS process with 130 nm gate length. The same low leakage current level is demonstrated for Sb and As extensions.
In situ Mg surface treatment of p-type GaN grown by ammonia-molecular-beam epitaxy for efficient Ohmic contact formation
Authors: Tang H. , Bardwell J. A. , Webb J. B. , Rolfe S. , Liu Y. , Moisa S. , Sproule I.
Published: January 2003

The pronounced effect of in situ Mg surface treatment of p-type GaN grown by ammonia-molecular-beam epitaxy on Ohmic contact formation is reported. The surface of the Mg-doped p-type GaN layer was held at the growth temperature following the growth, and exposed to a Mg beam under a NH3 flow for 15 min. With such a treatment, a specific contact resistance in the low 10−4 Ω cm2 was obtained with as-deposited Ni/Au contacts and without any ex situ treatment. In contrast, contacts on similar p-type layers without such an in situ treatment were highly rectifying even after annealing. A surface Fermi level shift as a result of the in situ treatment was observed by x-ray photoemission studies, and is ascribed, together with the high surface doping concentration, to be the mechanisms behind the effective Ohmic contact formation.
Fundamental optical absorption edge of undoped tetragonal zirconium dioxide
Authors: Aita C. R. , Hoppe E. E. , Sorbello R. S.
Published: January 2003

The high-frequency optical absorption edge of pure tetragonal ZrO2, isolated in a ZrO2–Al2O3 nanolaminate film structure, was determined using transmission spectrophotometry. The functional dependence of the absorption coefficient on photon energy shows two interband transitions: an initial indirect transition at 5.22 eV (i.e., the band gap) followed by a direct transition at 5.87 eV. The edge structure is associated with O 2p→Zr 4d electron states and discussed in terms of ab initio calculations reported in the literature.
Natural-superlattice-structured Bi4Ti3O12–SrBi4Ti4O15 ferroelectric thin films
Authors: Shibuya Akira , Noda Minoru , Okuyama Masanori , Fujisawa Hironori , Shimizu Masaru
Published: January 2003

Natural superlattice structures of c-axis-oriented Bi4Ti3O12–SrBi4Ti4O15 epitaxial ferroelectric thin films have been grown by pulsed laser deposition on both MgO (001) and SrTiO3 (001) substrates. The epitaxial growth of natural-superlattice-structured Bi4Ti3O12–SrBi4Ti4O15 thin film was confirmed by x-ray diffraction (XRD) θ–2θ scan, pole figure plots, and reciprocal space mappings. The c-axis lattice parameter of the Bi4Ti3O12–SrBi4Ti4O15 thin film became the average of those for Bi4Ti3O12 and SrBi4Ti4O15. The Bi4Ti3O12–SrBi4Ti4O15 thin film on Pt substrate shows that twice remanent polarization (2Pr) and coercive field (2Ec) are 32 μC/cm2 and 190 kV/cm, respectively.
Observation of a localized electron beam in large-area microwave discharge
Authors: Terebessy Tibor , Širý Milan , Kando Masashi , Kudela Jozef , Korzec Dariusz
Published: January 2003

We report on a localized high-density electron beam in large-area microwave discharges in argon. The beam is observed only for certain antenna configurations at gas pressures of about 50 mTorr, and it strongly modifies the radial plasma density profiles. The beam current near the quartz plate is estimated to be ≈140 mA/cm2.
Higher education and civic engagement*
Authors: Egerton Muriel
Published: January 2003

This paper focuses on the relationship between social engagement, particularly civic engagement, and education. It is well known that more highly educated people are more likely to engage in voluntary work in formalized settings. It has been difficult to disentangle the effect of higher education from that of family origin and occupational socialization. This paper examines the effects of tertiary education on the social and civic engagement of young people, using the British Household Panel Study. The social and civic activity of young people is observed in their late teens, before entering the labour market or tertiary education, and compared with that of the same young people in their early 20s, after completing tertiary education courses or gaining labour market experience. It was found that the social and civic engagement of young people who would enter higher education was higher in their late teens than that of their peers who did not enter. However, higher education had a small additional effect on civic engagement, for both young and mature students. The children of professionals were the social grouping most likely to be involved in civic activities. The relationship of higher education, professional occupations and family socialization is discussed.
Positivism in sociological research: USA and UK (1966–1990) 1
Authors: Gartrell C. David , Gartrell John W.
Published: January 2003

Positivism has been declared dead in sociological theory circles, yet questions remain as to its viability among researchers. The authors present diagnostic evidence about positivism in sociological practice through a content analysis of journal articles published in the late 1960s and the late 1980s in the sociological journals of the USA and Britain. Using an index based on seven elements of positivism that were characteristic of the ‘theory construction’ movement of the late 1960s, the authors find evidence of the effects of time and nation on the use of positivism. Disaggregation of the index reveals that most of the observed change is associated with the elements of ‘instrumental’ positivism, particularly statistics. The results raise questions about the relationship between theory and research and about sociologists’ philosophies of science.
Complexity and practical knowledge in the social sciences: a comment on Stehr and Grundmann
Authors: Meagher Gabrielle , Wilson Shaun
Published: January 2003

This paper takes issue with Stehr and Grundmann's argument in this journal that sociology's poor record of contribution to practical knowledge results from sociologists’ misguided attachment to the idea that social phenomena are peculiarly complex, and so peculiarly resistant to efforts at practical knowledge formation. Stehr and Grundmann develop their thesis by contrasting sociology to economics, claiming the latter's superior methods and disciplinary cultures enable it to contribute more successfully to solving practical problems. We argue that Stehr and Grundmann's comparison of the relative success of economics and sociology as policy sciences underestimates the extent to which the complexity argument has been destructive of economics’ capacity to contribute practical knowledge, and overestimates the importance of disciplinary methods and cultures in explaining the use of economics in policy making. Further, we argue that the ‘complexity argument’ can contribute to better policy making, by virtue of its capacity to high‐light the dangers of simplistic or fundamentalist solutions to social problems with complex causes.
Hepatic Toxicity and Recovery of Fischer 344 Rats Following Exposure to 2-Aminoanthracene by Intraperitoneal Injection
Authors: Baker David G. , Wayne Taylor H. , Lee Stephen P. , Barker Steven A. , Goad Mary E.P. , Means Jay C.
Published: January 2003

Humans may be exposed to 2-aminoanthracen e (2-AA), a substituted polycyclic aromatic hydrocarbon, and a recognized mutagen and carcinogen, through oral and respiratory routes from contact with a variety of environmental sources. For the present study, we sought to evaluate hepatic damage and recovery in Fischer 344 rats following multiple IP injections of 5 mg of 2-AA. Rats were injected weekly for up to 5 weeks. Subgroups were then allowed to recover for 1, 5, or 9 weeks, and biochemical and pathologic changes were evaluated. We observed that weight gains were reduced relative to controls for all groups receiving ≥ 2 injections. Serum enzyme levels indicative of liver damage were evident and included alterations in serum aspartate aminotransferase, alkaline phosphatase, total protein, albumin, and globulin. These alterations usually returned to normal by 5 weeks following cessation of 2-AA administration. In contrast, histologic liver changes, including hepatocyte hypertrophy, biliary hyperplasia with oval cell proliferation, altered foci, nodular hyperplasia, and one hepatocellular adenoma became more severe with time. This experiment demonstrates patterns of hepatic damage and recovery in rats exposed to 2-AA.
Suppression of Arylamine Toxicity in the Fischer-344 Rat Following Ingestion of a Complex Mixture
Authors: Boudreau Mary D. , Baker David G. , Taylor H. Wayne , Barker Steven A. , Means Jay C.
Published: January 2003

The toxic effects of a mixture of 2-aminoanthracene (2-AA), benzanthracene (BA), and dinitropyrene isomers (DNP), and the toxic effects of these compounds individually, were investigated in the Fischer-344 rat following dietary exposure via a powdered basal diet. Animals were sacrifi ced at 14-, 30-, and 80-day s of dietary exposure. Exposure to dietary 2-AA alone induced anorexia, cachexia, variable mortality, and altered serum chemistry profi les in the F-344 rat. Reduced lymphocyte counts were also shown in rats exposed to 2-AA. A temporal pattern of effect of 2-AA dietary exposure was observed in the progression of hepatic lesions in exposed animals. Dietary exposure to either DNP isomers or BA at a 10-fold higher concentration in the diet, relative to 2-AA, did not induce detectable toxic responses.

However, exposure of rats to a mixture of 2-AA, BA, and DNP isomers (100 mg/kg, 1.0 g/kg, and 1.0 g/kg of diet, respectively) resulted in the attenuation of toxic effects when compared to exposure of F-344 rats to 2-AA alone. These results indicate that the toxic effects of 2-AA are suppressed by co-administration of DNP and BA and suggest that compound interactions need to be considered when predicting the toxic potential of specifi c environmental pollutants.
The Effects of Ad Libitum Overfeeding and Moderate and Marked Dietary Restriction on Age-Related Spontaneous Pancreatic Islet Pathology in Sprague—Dawley Rats
Authors: Molon-Noblot Sylvain , Keenan Kevin P. , Coleman John B. , Hoe Chao-Min , Laroque Philippe
Published: January 2003

This study compared the effects of ad libitum (AL) overfeeding and moderate or marked dietary restriction (DR) on aged-related degenerative and proliferative changes of the endocrine pancreas in Sprague—Dawley (SD) rats. SD rats were fed Purina Certified Rodent Diet AL (group 1), DR at 72—79% of AL (group 2), DR at 68—72% of AL (group 3) or DR at 47—48% of AL (group 4) for 106 weeks. Interim necropsies were performed at 13, 26, and 53 weeks, after a 7-day 5-bromo-2-deoxyuridin e (BrdU)-filled minipump implantation. Before each necropsy, glucose and serum insulin levels were measured. In addition to the routine histopathologic examination performed in both sexes, determination of 9 pancreatic islet stereologic parameters was done in males at 13, 26, and 53 weeks. In AL-fed rats, early changes in the islet morphology occurred, which resulted in a high incidence of islet fibrosis, focal hyperplasias and adenomas by two years. DR was dose-proportionally associated with decreased glucose and serum insulin levels, and delayed the onset, and decreased the incidence and severity of islet fibrosis and hyperplasia. Results of the stereology supported the histopathologic and clinical chemistry findings. It demonstrated that, compared to AL-fed rats, DR-fed rats had smaller pancreas, smaller pancreatic islets, smaller insulin secreting cell volumes, a lower degree of islet fibrosis and a lower islet cell BrdU labeling index, which correlated with a lower incidence of islet adenoma and carcinoma at study termination. Moderate and marked degrees of DR delayed the onset and severity of islet hyperplasia and fibrosis in a temporal- and dose-related manner. In contrast to marked DR, which dramatically prevented these changes, moderate DR delayed but not prevented onset of islet tumors. These findings support the concept that moderate DR results in a better-controlled animal model with a lower incidence or delayed onset of chronic spontaneous endocrine diseases in the rat bioassay.
Metastasizing Neuroblastomas from Taste Buds in Rats Transgenic for the Simian Virus 40 Large T Antigen under Control of the Probasin Gene Promoter
Authors: Asamoto Makoto , Hokaiwado Naomi , Cho Young-Man , Ikeda Yoshihisa , Takahashi Satoru , Shirai Tomoyuki
Published: January 2003

During establishment of a prostate cancer model in rats transgenic for the Simian virus 40 large T antigen, under control of the probasin gene promoter, with protein expression specific to the prostate, tongue, and spinal cord, undifferentiated small round cell tumors were frequently observed. Extensive examination of tongues of the transgenic rats, despite a macroscopically normal appearance, revealed the tumors to have come from taste buds of the papilla circumvallata and papilla foliata. The lesions were positive for the SV40 T antigen, PGP9.5 (ubiquitin C-terminal hydrolase), and synaptophysin, neuron and neuroendocrine markers. Morphologically and immunohistochemically, the tumors were diagnosed as neuroblastomas, considering the neuroepithelial origin. Histologically identical tumor cells in the spinal cord and lung were observed only in the rats with deeply invading tongue tumors, suggesting that metastasis from the tongue tumors had occurred. Castration or supplementation with testosterone propionate did not alter tumor development, indicating the tumors to be androgen-independent . These results clearly show that taste buds can give rise to metastasizing neuroblastomas.
Cellular and Cytokine Responses in the Circulation and Tissue Reactions in the Lung of Rhesus Monkeys (Macaca mulatta) Pretreated with Cyclosporin A and Challenged with Staphylococcal Enterotoxin B
Authors: Komisar Jack L. , Weng Ching-Feng , Oyejide Adelekan , Hunt Robert E. , Briscoe Crystal , Tseng Jeenan
Published: January 2003

Cyclosporin A (CsA), an inhibitor of T cell cytokine production, protects mice against staphylococca l enterotoxin B (SEB) intoxication. To determine whether CsA treatment would work in a species closer to humans, 4 rhesus monkeys were given 50 mg/kg CsA followed by an intratracheal challenge with approximately 6 LD50 of SEB. The CsA was not protective: one of the monkey s died and the other three had to be euthanized when they became moribund. All monkeys made IL-2, TNF, and IFN- γ in response to SEB. In addition, there was about a 10-fold increase in ACTH levels 2 hr after SEB challenge. CsA significantly suppressed in vitro proliferation of lymphocytes from treated monkeys. Both CsA-treated monkeys and monkeys that had been challenged in a previous experiment with a lethal dose of SEB but had received no cyclosporin had pathologic changes in several organs. The most prominent changes were marked edema and leukocytic infiltration of the bronchial and bronchiolar mucosa. The CsA treatment appeared to reduce the intensity of lung inflammation, but this effect was not sufficient to protect the monkeys. The results suggest that CsA alone may not be an effective therapeutic agent for humans suffering from SEB intoxication or gram-positive septic shock.
Dermal Carcinogenicity in Transgenic Mice: Effect of Vehicle on Responsiveness of Hemizygous Tg.AC Mice to Phorbol 12-Myristate 13-Acetate (TPA)
Authors: Stoll Raymond E. , Furst Sylvia M. , Stoltz James H. , Lilly Patrick D. , Mennear John H.
Published: January 2003

The Tg.AC mouse is being evaluated for use in short-term carcinogenicity bioassays. Because the dermal test protocol necessitates dissolving test agents we determined the effects of several solvents on responsivenes s of hemizygous mice to dermal applications of the classical skin tumor promoter, phorbol 12-myristate 13-acetate (TPA). Mice of both sexes received dermal applications of either acetone (negative control) or TPA in various vehicles [acetone, 100% methanol, 70% and 100% ethanol, DMSO and mixtures of acetone and ethanol (1:1), acetone and DMSO (4:1 and 1:1), and acetone and olive oil (4:1)]. Negative control animals did not exhibit papillomas. When administered in acetone, ethanolic or methanolic vehicles TPA caused prompt and robust papillomatous responses. TPA was also tumorigenic in all nonalcoholic vehicles, except the acetone-olive oil mixture. Papilloma responses were generally delayed when TPA was applied in the nonalcoholic solvents but the distinction between TPA-dosed and negative control groups was unequivocal. These results show that choice of vehicle may affect the quantitative and qualitative nature of the response of Tg.AC mice to TPA, but 8 of 9 vehicles proved satisfactory for delivery of TPA.
Review Article: A Review of Chronic Inhalation Studies with Mainstream Cigarette Smoke, in Hamsters, Dogs, and Nonhuman Primates
Authors: Coggins Christopher R.E.
Published: January 2003

This paper is the continuation of previously published work, a review limited to studies on rats and mice. This paper makes an identical evaluation as before, but, restricting the species being evaluated to representative studies of smoke-exposed hamsters, dogs (both by tracheostomy and by direct inhalation), and nonhuma n primates. As was seen previously, no statistically significant increase in the incidence of malignant tumors of the respiratory tract was found in any of the 3 species, even though very long exposures and high doses of smoke were used. All 5 of the species of laboratory animals commonly used to evaluate carcinogenic potential produce results with mainstream cigarette smoke that are at variance with the epidemiological evidence in smokers.
Salt Water-Acclimated Pink Salmon Fry (Oncorhynchus gorbuscha) Develop Stress-Related Visceral Lesions after 10-Day Exposure to Sublethal Concentrations of the Water-Soluble Fraction of North Slope Crude Oil
Authors: Brand Dawna G. , Fink Ron , Bengeyfield William , Birtwell Ian K. , Mcallister Carry D.
Published: January 2003

Pink salmon fry, Oncorhynchus gorbuscha, after a 10-day exposure to one of two sublethal concentrations (25—54 μg·L-1 or 178—348 μg·L -1) of the water-soluble fractions from Alaska North Slope crude oil, possessed morphologic and stress induced lesions in their hepatic, head kidney and gill tissues. Analysis of livers from oil-exposed fry revealed a variety of hepatocellular changes, including steatosis, nuclear pleomorphism, megalocytosi s and necrosis. Epithelial proliferation of the bile ducts also occurred. An increase in the head kidney's interrenal cell nuclear diameter, a biomarker for stress responses, was correlated with hydrocarbon exposure. Gill abnormalities such as eqithelial lifting, fusion, mucous cell hyperplasia and vascular constriction were found in all test groups, but were more severe in fry given the high water soluble fraction of crude oil. The study demonstrated that sublethal exposure to the water-soluble fraction of crude oil results in multiple microscopic lesions (in several viscera) that are consistent with a pronounced response to environmental stress.