bluuebunny/crossref_metadata_2025 huggingface dataset:
Target strength of mesopelagic lanternfishes (family Myctophidae) based on swimbladder morphology
Authors: Yasuma Hiroki , Sawada Kouichi , Ohshima Tatsuki , Miyashita Kazushi , Aoki Ichiro
Published: June 2003

This article reports theoretical values of target strength (TS) for mesopelagic lanternfishes based on morphological measurements of their swimbladders. Three species of lanternfishes, Diaphus theta (26.9–77.4 mm standard length (SL)), Symbolophorus californiensis (85.0–108.4 mm SL), and Notoscopelus japonicus (126.0–133.2 mm SL), were examined. After external morphological measurement of the fish body, a specialized “soft X-ray” imaging system was used to map the swimbladders and obtain their morphological parameters. The swimbladder was inflated in D. theta, uninflated in S. californiensis, and was absent in N. japonicus. For D. theta, the swimbladder length does not increase in proportion to the body length, suggesting that the contribution of the swimbladder to acoustic reflection is reduced with growth in this fish. Based on the morphological measurements, the theoretical TS of the fish at 38 kHz was calculated using the approximate deformed-cylinder model (DCM) and the general prolate-spheroid model (PSM). For all three species, the calculations showed about 3 dB difference between the TS indicated by the DCM and PSM. Given that the description of body shape is poor in PSM, the DCM results were adopted for fish without a swimbladder or an empty one. The intercept b20 in the standard formula TS = 20 log SL + b20 was −85.7 dB (DCM) for S. californiensis and −86.7 dB (DCM) for N. japonicus. On the other hand, the PSM model was adopted for D. theta since its swimbladder has too small an aspect ratio to apply the DCM. For D. theta, the relationship between SL and TS is best expressed by TS = 11.8 log SL − 63.5, which implies that its scattering cross-section is not proportional to the square of the body length.
β‐Blocker treatment of patients with diastolic heart failure and arterial hypertension. A prospective, randomized, comparison of the long‐term effects of atenolol vs. nebivolol
Authors: Nodari Savina , Metra Marco , Dei Cas Livio
Published: June 2003

We compared the effects of 6 months administration of atenolol or nebivolol on resting and exercise hemodynamic parameters and maximal exercise capacity, in 26 patients with hypertension and left ventricular (LV) diastolic dysfunction (ejection fraction >50%, end‐diastolic diameter <60 mm and increased pulmonary wedge pressure at rest and/or at peak exercise). Both atenolol and nebivolol administration was associated with a significant decrease in the resting and peak exercise heart rate and blood pressure and in LV mass, with an increase in the E/A ratio. This latter effect was greater with nebivolol. Nebivolol was associated with an increase in the peak VO2, VO2 at the anaerobic threshold and with a decrease in the VE/VCO2 ratio. With regards to the hemodynamic parameters, compared to patients on atenolol, those on nebivolol showed a lower reduction in the cardiac index, a greater increase in the stroke volume index and a decline in the mean pulmonary artery pressure and pulmonary wedge pressure, both at rest and peak exercise. Thus, although the two β‐blockers have a similar antihypertensive action, nebivolol administration was associated with a greater hemodynamic improvement, compared to atenolol.
Trace element abundances of Mauna Kea basalt from phase 2 of the Hawaii Scientific Drilling Project: Petrogenetic implications of correlations with major element content and isotopic ratios
Authors: Huang S. , Frey F. A.
Published: June 2003

The temporal geochemical variations defined by lavas erupted throughout the growth of a single volcano provide important information for understanding how the Hawaiian plume works. The Hawaii Scientific Drilling Project (HSDP) sampled the shield of Mauna Kea volcano to a depth of 3100 meters below sea level during Phase 2 of the HSDP. Incompatible element abundance ratios, such as La/Yb, Sm/Yb, Nb/Zr, and Ti/Zr, in conjunction with SiO2 abundance and radiogenic isotopic ratios, especially He and Pb, in the reference sample suites of the Mauna Kea portion of cores from Phases 1 and 2 of the HSDP define three distinct geochemical groups. The upper 550 m of Mauna Kea lavas in the Phase 2 core include the Postshield Group with eruption ages of ∼200 ka to <370 ka. These lavas have relatively low SiO2 content, 3He/4He and 206Pb/204Pb, and they define a trend to relatively high La/Yb, Sm/Yb, and Nb/Zr. The eruption of these lavas coincides with migration of the Mauna Kea shield off the hot spot. As a result, extent of melting decreased, melt segregation occurred at greater depth, within the garnet stability field, and a geochemically distinct component associated with the periphery of the plume was sampled. Deeper in the Phase 2 core two other geochemical groups of lava are intercalated. One group has relatively low SiO2 abundance and high Nb/Zr Ti/Zr, 3He/4He and high 208Pb/204Pb at a given 206Pb/204Pb. These are distinctive geochemical characteristics of lavas erupted at Loihi seamount. Variations in incompatible element abundance ratios (e.g., Sm/Yb versus Nb/Zr and La/Yb versus Ti/Zr) define mixing trends between these low SiO2 lavas (Loihi‐type) and lavas belonging to a high SiO2 group that are the dominant lava type in the shield part of the core (Kea‐type). These two groups are presumed to reflect components intrinsic to the plume. Correlations of incompatible element abundance ratios, such as La/Nb, with radiogenic isotope ratios show that Hawaiian shields contain different proportions of geochemically distinctive components. The Koolau shield contains a recycled sedimentary component that is not present in the Mauna Kea shield. The anomalously high Ba/Th in Hawaiian lavas is inferred to be a source characteristic. Ba/Th is correlated with some radiogenic isotope ratios in Kilauea and Mauna Loa lavas, but there is no correlation in Mauna Kea lavas which range in Ba/Th by a factor of 2.6.
Large parallel electric fields in the upward current region of the aurora: Evidence for ambipolar effects
Authors: Hull A. J. , Bonnell J. W. , Mozer F. S. , Scudder J. D. , Chaston C. C.
Published: June 2003

Electric fields parallel to the magnetic field play a major role in the transport of mass, momentum, and energy in the auroral zone. In this paper we explore which terms of the steady state electron momentum equation are consistent with the large‐amplitude, macroscopic parallel electric fields (∼25 mV/m to 300 mV/m) measured by the electric field instrument on Polar in the upward current part of the auroral acceleration region. From a detailed analysis of eight events we found evidence suggesting that the large‐amplitude, macroscopic parallel electric fields are ambipolar in character; namely, they are supported by electron pressure gradients present at the interface separating the relatively cold, dense ionospheric plasma from the hot, tenuous magnetospheric plasma in the auroral density cavity. These structures do not appear to be explained by purely propagating Alfvén waves. These large‐amplitude, macroscopic parallel electric fields are likely to be a sheath field that forms at the boundary separating a high and low density plasma, similar to that encountered in laboratory experimental devices.
On the nonlinear integral transform of an ocean wave spectrum into an along‐track interferometric synthetic aperture radar image spectrum
Authors: He Yijun , Alpers Werner
Published: June 2003

We present a new nonlinear integral transform relating the ocean wave spectrum to the along‐track interferometric synthetic aperture radar (AT‐INSAR) image spectrum. The AT‐INSAR, which is a synthetic aperture radar (SAR) employing two antennas displaced along the platform's flight direction, is considered to be a better instrument for imaging ocean waves than the SAR. This is because the AT‐INSAR yields the phase spectrum and not only the amplitude spectrum as with the conventional SAR. While the SAR and AT‐INSAR amplitude spectra depend strongly on the modulation of the normalized radar cross section (NRCS) by the long ocean waves, which is poorly known, the phase spectrum depends only weakly on this modulation. By measuring the phase difference between the signals received by both antennas, AT‐INSAR measures the radial component of the orbital velocity associated with the ocean waves, which is related to the ocean wave height field by a well‐known transfer function. The nonlinear integral transform derived in this paper differs from the one previously derived by Bao et al. [1999] by an additional term containing the derivative of the radial component of the orbital velocity associated with the long ocean waves. By carrying out numerical simulations, we show that, in general, this additional term cannot be neglected. Furthermore, we present two new quasi‐linear approximations to the nonlinear integral transform relating the ocean wave spectrum to the AT‐INSAR phase spectrum.
Limitations of using an equilibrium approximation in an aerosol activation parameterization
Authors: Phinney Lisa A. , Lohmann Ulrike , Leaitch W. Richard
Published: June 2003

Because of its complex nature, attempts have been made to parameterize the process of cloud droplet formation and growth. The parameterization developed by Abdul‐Razzak et al. [1998] and Abdul‐Razzak and Ghan [2000], henceforth referred to as the ARG parameterization, is based on the adiabatic ascent of an air parcel, assuming that each particle is in equilibrium with its environment. Some of the limitations of the equilibrium assumption are evaluated here through direct comparison of a kinetic parcel model with the ARG parameterization. Conditions are described in which the supersaturation and the cloud droplet number concentration are underpredicted by the parameterization. The underprediction happens because of an overestimation of the condensation rate of water onto the larger particles. The effect is significant for conditions of lower updraft velocities (V < 50 cm s−1) and higher aerosol number concentrations (Na > 500 cm−3). The parameterization behaves well for higher updraft velocities and lower aerosol number concentrations. The impact of this effect on the activation of sulfate aerosols in the presence of sea salt aerosol is also investigated. Using the ARG parameterization to diagnose Nd in the presence of sea salt aerosol leads to a greater reduction in the number of activated sulfate particles in lower updraft conditions than does using the kinetic parcel model. The relative contribution of sulfate particles to total Nd is also significantly lower for the ARG parameterization than it is for the parcel model in low to moderate updrafts. The error in the first indirect radiative forcing introduced by the equilibrium assumption is estimated to be 6 to 15 W m−2 for typical marine clouds, depending on the updraft velocity.
Magnetic resonance imaging of dense and light non‐aqueous phase liquid in a rock fracture
Authors: Becker Matthew W. , Pelc Matthew , Mazurchuk Richard V. , Spernyak Joseph
Published: June 2003

Magnetic resonance (MR) imaging was used to observe the flow of dense (FC‐75) and light (dodecane) non‐aqueous phase liquids (NAPLs) through a water saturated dolomite fracture. Dynamic two‐phase behavior was influenced by (1) buoyancy of the NAPL relative to the aqueous phase, (2) fracture aperture distribution, and (3) alteration of wettability by long‐term presence of NAPL phase. MR imaging was capable of characterizing the fracture geometry and the fluid flow, but was limited by outlet flow conditions in the sample and acquisition times. This method permits observation of two‐phase flow under natural wettability and matrix porosity, providing significant advantages over plastic or glass replicas.
The outer limits of the lunar sodium exosphere
Authors: Wilson Jody K. , Baumgardner Jeffrey , Mendillo Michael
Published: June 2003

A new wide‐angle coronagraphic‐type imaging system used for the lunar eclipse of 16 July 2000 resulted in detections of the lunar sodium exosphere out to ∼20 lunar radii, approximately twice the size recorded with narrower fields of view during previous eclipses. These measurements and subsequent modeling provide a unique constraint on the fastest atoms ejected from the lunar surface that form the lunar exosphere, indicative of the most energetic space weathering processes acting on the lunar surface. At most, only a small fraction of the atoms are ejected from the surface with speeds faster than escape speed of 2.4 km s−1, meaning solar photon radiation pressure largely contributes to the escape of sodium atoms which form the comet‐like tail. The total rate of sodium ejection from the surface for speeds >2.0 km s−1 is comparable to estimates from previous lunar eclipse observations and earlier images of the lunar sodium tail.
Using the 630.0‐nm nightglow emission as a surrogate for the ionospheric Pedersen conductivity
Authors: Makela Jonathan J. , Kelley Michael C.
Published: June 2003

We develop a technique to create two‐dimensional maps of the field line integrated, F‐layer Pedersen conductivity from images of the 630.0‐nm emission at midlatitudes. By modeling the 630.0‐nm and the height‐integrated Pedersen conductivity, we show that the former can be used as a surrogate for the latter to within 0.2 mhos if information on the height of the F‐layer is known. A simple thin‐shell model is used to convert the height‐integrated conductivity to field line integrated conductivity, a more useful parameter in the study of midlatitude ionospheric dynamics. Two nights are studied using this technique, one with a gradient in electron density seen to the south and one with severe depletions. In the latter case, bands of alternating low and high field line integrated Pedersen conductivity are seen to align from the northwest to southeast, just as predicted by Perkins [1973].
Simulation of hot oxygen effects on ground‐based Fabry‐Perot determinations of thermospheric temperatures
Authors: Sipler D. P. , Biondi M. A.
Published: June 2003

The response of a ground‐based Fabry‐Perot interferometer (FPI) to predicted non‐Maxwellian energy distributions of atomic oxygen in the F region is calculated. Analysis of the simulated profiles shows that the high‐energy component of the non‐Maxwellian profiles has a modest effect on ground‐based measurements, raising the temperature derived from the Doppler‐broadened profiles above that of the thermosphere in the 630 nm emission region. The effect is small compared to the uncertainties for an individual measurement but could be significant when large numbers of profiles are averaged in an attempt to reduce uncertainties in the determinations. However, the effect cannot account for the >100 K difference between the FPI determinations and values derived from empirical models such as the Mass Spectrometer Incoherent Scatter model.
Metric 3D Structure in Visualizations
Authors: Lind Mats , Bingham Geoffrey P. , Forsell Camilla
Published: June 2003

A large body of results on the characteristics of human spatial vision suggests that space perception is distorted. Recent studies indicate that the geometry of visual space is best understood as affine. If this is the case, it has far-reaching implications on how 3D visualizations can be successfully employed. For instance, all attempts to build visualization systems where users are expected to discover relations based on Euclidean distances or shapes will be ineffective. Since visualization can, and sometimes does, employ all possible types of depth information and because the results from vision research usually concentrates on one or two such types, three experiments were performed under near-optimal viewing conditions. The aim of the experiments was two-fold: to test whether the earlier findings generalize to shape perception under near-optimal viewing conditions and to get a sense of the size of the error under such conditions. The results show that the findings do generalize and that the errors are large. The implications of these results for successful visualizations are discussed.
Negative bias temperature instability: Road to cross in deep submicron silicon semiconductor manufacturing
Authors: Schroder Dieter K. , Babcock Jeff A.
Published: June 2003

We present an overview of negative bias temperature instability (NBTI) commonly observed in p-channel metal–oxide–semiconductor field-effect transistors when stressed with negative gate voltages at elevated temperatures. We discuss the results of such stress on device and circuit performance and review interface traps and oxide charges, their origin, present understanding, and changes due to NBTI. Next we discuss the effects of varying parameters (hydrogen, deuterium, nitrogen, nitride, water, fluorine, boron, gate material, holes, temperature, electric field, and gate length) on NBTI. We conclude with the present understanding of NBTI and its minimization.
Relativistic Gaussian basis sets for molecular calculations: Tl–Lr
Authors: Koga Toshikatsu , Tatewaki Hiroshi , Matsuoka Osamu
Published: June 2003

Relativistic four-component Gaussian basis sets are developed for the 23 atoms Tl81–Lr103. The total energies of these basis sets are slightly below the corresponding numerical Dirac–Fock values. Test calculations conclude, however, that the present basis sets could be used safely in molecular applications.
sp
3
/sp
2
ratio in amorphous-carbon thin film by spectroscopic ellipsometry
Authors: Li W. J. , Song Z. R. , Yu Y. H. , Wang X. , Zou S. C. , Shen D. S.
Published: June 2003

We introduce tetrahedral amorphous-carbon thin films, formed by reactive filtered arc deposition method, as a dielectric material for a silicon-on-insulator substrate in high-power integrated circuits. The sp3/sp2 components in the thin films were measured by spectroscopic ellipsometry, which is well known for its nondestructive and in situ characterization application. The dielectric functions of the composite materials were calculated using the Bruggeman effective medium approximation. The surface roughness was studied through atomic force microscopy. Also, the film content and thickness was studied by Rutherford backscattering.
Low-energy electron scattering by methylsilane
Authors: Bettega M. H. F. , Winstead C. , McKoy V.
Published: June 2003

We report calculated elastic and inelastic cross sections for low-energy electron collisions with methylsilane, CH3SiH3, obtained using the Schwinger multichannel method. The elastic cross sections, obtained within the static-exchange approximation, are compared with elastic results for C2H6 and Si2H6. Electron-impact excitation cross sections were computed for sixteen electronic states arising from excitation out of the two highest-lying valence orbitals. The dissociation of the lowest few states was examined through limited electronic-structure calculations, which indicated that the 2 1,3A1 states dissociate to CH3SiH+H2 while the 1 1,3E states dissociate to CH3+SiH3.
Fine-structure effects in vibrational relaxation at ultralow temperatures
Authors: Volpi Alessandro , Bohn John L.
Published: June 2003

We have calculated cross sections for vibrational quenching in collisions of O217(X 3∑g−) with He3 at cold and ultracold temperatures, explicitly accounting for the electronic spin degree of freedom. The observed population of the final spin-rotational levels can be interpreted on the basis of useful “propensity rules” governing the intensity of the collision-induced transitions. In addition, it is found that the orientation of the molecular spin is reasonably robust against collisional relaxation, even in vibrationally excited states. This finding implies that magnetic trapping of vibrationally excited, but rotationally and translationally cold, molecules may be possible.
Structural, electronic, and vibrational properties of solid Sr(OH)2, calculated with different Hamiltonians
Authors: Mérawa Mohammadou , Civalleri Bartolomeo , Ugliengo Piero , Noël Yves , Lichanot Albert
Published: June 2003

The structural equilibrium parameters, the energetic of formation and hydration processes, and the O–H vibrational frequencies of crystalline Sr(OH)2 have been investigated at the ab initio level using the periodic CRYSTAL package. Both Hartree–Fock (HF) and density functional theory (DFT) Hamiltonians have been used, the latter in its local density (LV), gradient-corrected (PP), and hybrid (B3LYP) versions. The computed Sr(OH)2 structural parameters are in reasonable agreement with experiment, the largest deviation being for the a cell parameter, which is overestimated by all the adopted methods. With respect to experiment, DFT Hamiltonians give errors of the order of 13% for the formation energies, whereas errors for the heats of hydration from the corresponding oxide are as large as 27% for the LV functional. Two families of OH groups occur in the structure, in which one acts as a weak hydrogen bond donor. The fundamental ω01(OH) stretching frequency has been computed for the two OH groups, and their difference compared to experiment is (i) severely overestimated by HF, (ii) underestimated by both LV and PP, and (iii) in fair agreement at the B3LYP level. As a function of the adopted method, good correlation exists between ω01(OH) and (i) the OH equilibrium bond length, (ii) the OH⋯O H bond angle, and (iii) the value of the electric field gradient calculated at the H nucleus. Among the adopted functionals, B3LYP performs best for all considered features, particularly so for the OH vibrational data.
Transport beam line for ultraslow monoenergetic antiprotons
Authors: Franzen K. Yoshiki , Kuroda N. , Torii H. A. , Hori M. , Wang Z. , Higaki H. , Yoneda S. , Juhász B. , Horváth D. , Mohri A. , Komaki K. , Yamazaki Y.
Published: June 2003

A beam line for the transportation of slow antiprotons from a multiring electrode trap to an experimental chamber is described. The beam line is equipped with a three-stage differential pumping system in order to maintain a pressure lower than 1×10−12 Torr in the trap region while simultaneously having a pressure of around 1×10−6 Torr in the chamber. Tests have shown that 105 positive ions per trapping cycle were successfully extracted at 250 eV from the trap positioned in a superconducting solenoid. The ions were then further transported through three small apertures to the target area located 3.5 m downstream of the trap. Results from the first delivery of a 250 eV antiproton beam are described.
Normal-mode analysis without the Hessian: A driven molecular-dynamics approach
Authors: Bowman Joel M. , Zhang Xiubin , Brown Alex
Published: June 2003

We point out that normal modes and frequencies of molecules and molecular complexes can be obtained directly from a harmonically driven molecular dynamics calculation. We illustrate this approach for HOD and H5O2+ and then discuss its potential advantages over the standard Hessian-based approach for large molecules.
Continuous wave cavity ring-down spectroscopy applied to in situ detection of dinitrogen pentoxide (N2O5)
Authors: Simpson William R.
Published: June 2003

We describe an instrument using cavity ring-down spectroscopy (CRDS), an ultrasensitive detection method, to detect NO3 and N2O5 (via thermal dissociation to NO3 at 80 °C). We use continuous-wave (cw) cavity ring-down spectroscopy, allowing a highly reliable diode laser to act as the light source. This instrument uses all solid-state laser and optical components, and it is compact, portable, and power efficient. Advantages and disadvantages of cw CRDS compared to pulsed CRDS are discussed. Inlet losses and possible interferences were extensively investigated. We show field observations of N2O5 mixing ratios in ambient air. Dinitrogen pentoxide was measured because low ambient temperatures shift the equilibrium between NO3, NO2, and N2O5 strongly towards N2O5. Therefore, only N2O5 is assumed to be present in significant quantities in Fairbanks, AK, during winter. From these data, we identify times where the N2O5 mixing ratio must be zero (due to the absence of ozone indicating presence of NO) and use these time periods to measure the system’s operational detection limit. The 2σ detection limit for N2O5 is 2.4 parts per trillion by volume (pptv) in a 25 s average. Prediction of the N2O5 detection limit from estimates of ring-down signal noise indicates a detection limit of 1.6 pptv, in the same averaging period. The observed detection limit is about 50% larger than the predicted detection limit, indicating that other noise sources affect the true detection limit. A similar instrument using pulsed CRDS was described in the last year, and we compare our instrument to this instrument for detection of N2O5.
Temperature dependence of the impact ionization coefficients in GaAs, cubic SiC, and zinc-blende GaN
Authors: Tirino Louis , Weber Michael , Brennan Kevin F. , Bellotti Enrico , Goano Michele
Published: June 2003

In this article we discuss the effect of temperature on the impact ionization coefficients in wide band-gap semiconductors and compare it to that of bulk GaAs. The impact ionization coefficients as a function of temperature are examined for three semiconductors: gallium arsenide, cubic phase silicon carbide, and zinc-blende phase gallium nitride. It is found that the magnitude of the phonon energy is principally responsible for changes in the impact ionization coefficients as a result of temperature change. While the energy band gap of a material does have a temperature dependence that directly affects the impact ionization transition rate, that change is much smaller than the relative change in the magnitude of the phonon-scattering rates in all of the materials studied here. The phonon energies are found to play a vital role in the magnitude of the change in the scattering rates as a function of temperature. Materials with relatively small phonon energies have phonon scattering rates that change considerably with temperature, and therefore have impact ionization coefficients that also change considerably with changes in temperature. Conversely, the phonon scattering rate in materials with a large phonon energy is less affected and thus these materials have impact ionization coefficients that are relatively insensitive to changes in the temperature.
Quantum phase-space function formulation of reactive flux theory
Authors: Barik Debashis , Banik Suman Kumar , Ray Deb Shankar
Published: June 2003

On the basis of a coherent-state representation of the quantum noise operator and an ensemble averaging procedure a scheme for quantum Brownian motion has been proposed recently [Banerjee et al., Phys. Rev. E 65, 021109 (2002); 66, 051105 (2002)]. We extend this approach to formulate reactive flux theory in terms of quantum phase space distribution functions and to derive a time-dependent quantum transmission coefficient—a quantum analog of the classical Kramers–Grote–Hynes coefficient in the spirit of Kohen and Tannor’s classical formulation. The theory is valid for arbitrary noise correlation and temperature. The specific forms of this coefficient in the Markovian as well as in the non-Markovian limits have been worked out in detail for the intermediate to strong damping regimes with an analysis of quantum effects. While the classical transmission coefficient is independent of temperature, its quantum counterpart has significant temperature dependence particularly in the low-temperature regime.
Structural and electrical properties of (1−x)Bi(Ga1/4Sc3/4)O3–xPbTiO3 piezoelectric ceramics
Authors: Cheng Jinrong , Eitel Richard , Li Nan , Cross L. E.
Published: June 2003

Bismuth containing crystalline solutions (1−x)Bi(Ga1/4Sc3/4)O3–xPbTiO3 (BGS–PT) have been developed using conventional ceramic technology. X-ray diffraction analysis reveals that BGS-PT has a perovskite structure, in which tetragonal to rhombohedral phase transformation appears for x=0.6. The dielectric properties were investigated at room and elevated temperatures, respectively, for different PT contents. BGS–PT for x=0.6 shows enhancement in dielectric constant K and piezoelectric constant d33 of 1180 and 124 pC/N, respectively, for the compositions investigated. The Curie temperature (Tc) of BGS–PT is in the range of 465–510 °C at least 100 °C higher than that of conventional Pb(Zr,Ti)O3 piezoelectric ceramics. The coercive field (Ec) of BGS–PT strongly depends on the PT content and can reach 75 kV/cm for x=0.8. Our results show that BGS–PT is a good low-lead high-temperature piezoelectric ceramic.
Photoelectromagnetic effects on electron and proton irradiated CuInSe2 thin films
Authors: Lee Hae-Seok , Okada Hiroshi , Wakahara Akihiro , Yoshida Akira , Ohshima Takeshi , Itoh Hisayoshi
Published: June 2003

Photoelectromagnetic effects in CuInSe2 (CIS) thin films irradiated with 3 MeV electrons or 380 keV protons have been investigated to evaluate the diffusion length. CIS thin films were deposited by radio frequency sputtering. The diffusion length was decreased due to irradiation-induced defects, as the electron fluence exceeded 1×1016 cm−2. The damage constant was estimated from the change in diffusion length before and after irradiation, and was about 4×10−9. After proton irradiation, the diffusion length decreased significantly as the proton fluence exceeded 1×1013 cm−2. The damage constant in this case was estimated to be about 1×10−4–4×10−5.
High-resolution investigation of atomic interdiffusion during Co/Ni/Si phase transition
Authors: Alberti A. , Bongiorno C. , La Via F. , Spinella C.
Published: June 2003

We studied the phase transition of Co/Ni thin films on amorphous silicon using an approach based on in situ sheet resistance analyses during isothermal annealing processes. Compared to conventional Co/Si systems, Co/Ni/Si reaction produces a double peak in the resistance curve versus time. This behavior has been extensively studied by Rutherford backscattering spectroscopy, x-ray diffraction, energy filtered transmission electron microscopy, and selected area diffraction analyses. It has been found that the kinetic evolution of the Co/Ni/Si structure occurs through two consecutive transition stages which are strictly related to each of the resistance peaks. At the beginning, cobalt atoms remain confined at the surface while nickel reacts with silicon hence producing the occurrence of the first resistance peak. The second peak is instead related to the cobalt atoms diffusing through the grain boundaries of the underlying Ni2Si layer, converting Ni2Si in a continuos CoSi film and forming pipelines through the underlying NiSi down the substrate. As a result, a ternary compound nucleates in contact with silicon. The final structure at the plateau of the resistance curve is a multilayer of CoSi/NiSi/Co(Ni)Si2, different from the case of Co/Ni thick-layer reaction.
Phase behavior of charged lipid bilayer membranes with added electrolyte
Authors: Komura Shigeyuki , Shirotori Hisashi , Kato Tadashi
Published: June 2003

We investigate the phase behavior of the aqueous solution of charged lipid bilayer membranes forming a lamellar structure in the presence of the added electrolyte. The Goldstein–Leibler model [Phys. Rev. A 40, 1025 (1989)] proposed for neutral lipids is extended by taking into account the screened electrostatic interaction which belongs to the so called intermediate region of the Poisson–Boltzmann theory. We mainly focus on the variation of the phase behavior as the added electrolyte concentration is changed. By decreasing the electrolyte concentration, the electrostatic repulsion between the neighboring membranes becomes stronger. As a result, the maximum equilibrium swelling composition shifts to larger water content, and the lamellar repeat distance increases although the membrane thickness remains almost constant. Our results recover not only the experimentally observed phase diagram for the charged lipid, but also the dependence of the lamellar repeat distance both on the electrolyte concentration and on the lipid composition. Some discussions are provided for the case when the electrostatic interaction is not screened due to the absence of any electrolyte.
A Monte Carlo study of effects of chain stiffness and chain ends on dilute solution behavior of polymers. II. Second virial coefficient
Authors: Yamakawa Hiromi , Yoshizaki Takenao
Published: June 2003

A Monte Carlo (MC) study is made of the second virial coefficient A2 for polymers using two freely rotating chains, each of bond angle 109°, with the Lennard-Jones 6-12 intramolecular and intermolecular potentials between beads in a cutoff version for the number of bonds in the chain ranging from 6 to 1000 in the Θ and good-solvent conditions. It is found that effects of chain ends on A2 are appreciable for small molecular weight M, as was expected, and that the second virial coefficient A2,Θ at the Θ temperature, at which the ratio 〈S2〉/M of the mean-square radius of gyration 〈S2〉 to M becomes a constant independent of M for very large M, remains slightly negative even for such large (but finite) M where the effects of chain ends disappear. Such behavior of A2,Θ, which cannot be explained within the framework of the binary cluster theory, is shown to be understandable if possible effects of three-segment interactions are considered. The present MC data for A2 (along with the previous ones for 〈S2〉) may then be consistently explained by the existent theory based on the helical wormlike chain model only if a minor correction is made to the theoretical A2,Θ in almost the same range where the effects of chain ends are appeciable. The present MC data are also compared with experimental data, and it is shown that the latter may also be similarly explained.
Electron detachment energies in high-symmetry alkali halide solvated-electron anions
Authors: Anusiewicz Iwona , Berdys Joanna , Simons Jack , Skurski Piotr
Published: June 2003

We decompose the vertical electron detachment energies (VDEs) in solvated-electron clusters of alkali halides in terms of (i) an electrostatic contribution that correlates with the dipole moment (μ) of the individual alkali halide molecule and (ii) a relaxation component that is related to the polarizability (α) of the alkali halide molecule. Detailed numerical ab initio results for twelve species (MX)n− (M=Li,Na; X=F,Cl,Br; n=2,3) are used to construct an interpolation model that relates the clusters’ VDEs to their μ and α values as well as a cluster size parameter r that we show is closely related to the alkali cation’s ionic radius. The interpolation formula is then tested by applying it to predict the VDEs of four systems [i.e., (KF)2−, (KF)3−, (KCl)2−, and (KCl)3−] that were not used in determining the parameters of the model. The average difference between the model’s predicted VDEs and the ab initio calculated electron binding energies is less than 4% (for the twelve species studied). It is concluded that one can easily estimate the VDE of a given high-symmetry solvated electron system by employing the model put forth here if the α, μ and cation ionic radii are known. Alternatively, if VDEs are measured for an alkali halide cluster and the α and μ values are known, one can estimate the r parameter, which, in turn, determines the “size” of the cluster anion.
Self-assembly of epitaxial Ag nanoclusters on H-terminated Si(111) surfaces
Authors: Li B. Q. , Zuo J. M.
Published: June 2003

We report an experimental investigation on self-assembly of epitaxial Ag nanoclusters on H-terminated Si(111) surfaces. We show that epitaxial Ag clusters of 2–6 nm in diameter can be synthesized by depositing at room temperature, followed by in situ annealing. As-deposited Ag clusters are uniformly distributed on the surface with a well-defined minimum spacing. The Ag clusters are mostly single crystals with Ag(111)//Si(111). The in-plane orientation of the as-grown clusters has a dispersion of ∼9° centering around the Si[110] direction. Upon annealing, most Ag clusters rotate to the epitaxial orientation with Ag[110]//Si[110]. The nanocluster rotation and epitaxy are explained using the coincident site lattice model for the interface structure and interfacial energy minimization.
Physical mechanism for saturation of persistent photoconductivity in a GaAs–AlAs/GaAs single heterojunction
Authors: Prasad S.
Published: June 2003

The saturation in persistent photoconductivity (PPC) in a Si-doped GaAs–AlAs/GaAs heterostructure is investigated using magnetotransport technique at 4.2 K. Against the donor density of 1.2×1013 cm−2, the maximum electron concentration including the contribution from the two-dimensional channel after 1.41 eV illumination is found to be 7.9×1011 cm−2. This result is anomalous as the DX states are expected to respond to 1.41 eV photons so as to bring the electron density close to the donor density. In order to investigate this issue a high electron-mobility transistor has been fabricated. The channel of this device contains a Hall-bridge pattern. The capacitance–voltage in conjunction with quantum transport measurements reveals that at saturation of PPC a second channel of electron gas is present in GaAs–AlAs superlattice. Furthermore, this channel is a nonconducting one as the electrons in it do not participate in the transport process. The reason behind it is the presence of potential barriers that separate the electron gas in the superlattice (EGS) from the alloyed regions meant for ohmic contacts to two-dimensional electron gas (2DEG). The formation of these potential barriers is linked to the lateral diffusion of In atoms used to make ohmic contacts to 2DEG. At saturation of PPC the electron density of EGS and 2DEG together is found to be 2.2×1012 cm−2. The remaining donors are believed to form electronically inactive complexes. At saturation of PPC the two-dimensional electron density (n2D) is determined by the tunneling probability through the potential barrier adjacent to the alloyed region. During the course of this investigation n2D at 4.2 K measured in the dark was found to depend on the cooldown rate. This phenomenon is attributed to the formation of a nonconducting channel.
Optical absorption behavior of ZrO2–TiO2 nanolaminate films
Authors: Aita C. R. , DeLoach J. D. , Sorbello R. S.
Published: June 2003

The near-ultraviolet fundamental optical absorption edge of sputter-deposited ZrO2–TiO2 nanolaminate films on SiO2 substrates was studied by transmission-reflection spectrophotometry. Seven different bilayer architectures were investigated, with nominal ZrO2 volume fractions ranging from 0.10 to 0.91 (Zr atom fractions of 0.1–0.9). The absorption coefficient, α(E), was determined as a function of the incident photon energy, E, in the 3.5–5.8 eV range (350–215 nm wavelength). α(E) vs E curves show a systematic blueshift and a change in shape with an increase in the Zr atom fraction in a bilayer. Neither amalgamation nor persistence models can adequately explain the experimental results. The reason why is that an extensive and structurally complex mixed cation interfacial structure formed even during room temperature deposition. A model that takes into account contributions to α(E) from Ti–O–Ti and Zr–O–Zr linkages far from the interfaces between constituents and Ti–O–Zr linkages at these interfaces is successfully applied to the data.
Crosstalk problems in scanning-by-probe atomic force microscopy
Authors: Varenberg M. , Etsion I. , Halperin G.
Published: June 2003

Crosstalk problems in fixed optics scanning-by-probe atomic force microscopy are demonstrated by scanning a commercially available calibration grating. It is found that this scanning-by-probe scheme significantly distorts contact response detection, and may even indicate false cantilever deformation when the scanning unit grossly displaces an undeformed cantilever. A compensating electronic circuit that can successfully correct this distortion is presented.
Improved field emission at electric-discharge-conditioned sites on diamond surfaces due to the formation of carbon nanotubes
Authors: Koenigsfeld N. , Kalish R. , Hoffman A.
Published: June 2003

The role of local materials modification to field emission (FE) from diamond is studied. FE properties of a boron-doped hydrogenated diamond film containing an array of sp2 rich channels that extend from surface to substrate and of diamond films subjected to an electric discharge are reported. Whereas the implantation-graphitized regions do not show any improvement in emission properties, compared to unirradiated or fully irradiated regions of the same sample, much improved emission is found for all regions once conditioned by an electric discharge. We show that carbon nanowhiskers (most likely carbon nanotubes) were formed in the vicinity of all conditioned sites and can account for the improved emission following “conditioning” that have been reported for many carbon-based field emitters.
B-site disordering in Pb(Sc1/2Ta1/2)O3 by mechanical activation
Authors: Gao X. S. , Xue J. M. , Wang J. , Yu T. , Shen Z. X.
Published: June 2003

B-site disorder in Pb(Sc1/2Ta1/2)O3 (PST) is traditionally tailored by thermal annealing after sintering at elevated temperatures. In this letter, we report B-site disordering in PST triggered by mechanical activation (MA), and the resulting ferroelectric behaviors thus derived. MA induces B-site order–disorder transformation in PST, and more interestingly, the structural disorder can well be retained in sintered PST, leading to a change in ferroelectric transition behavior (e.g., from a normal ferroelectric to relaxor) and a shift in Curie temperature. A designed degree of disorder in PST can therefore be obtained by the effective combination of presinter MA and subsequent sintering, giving rise to the specific ferroelectric properties that are required for certain applications.
High-frequency direction finding in space
Authors: James H. G.
Published: June 2003

Transionospheric propagation experiments at high frequency (HF) are planned in the Enhanced Polar Outflow Probe small-satellite mission. Crossed dipoles connected to a HF receiver in the spacecraft will be used to measure parameters of incident waves originating from coordinated ground transmitters. This article is concerned with the measurement of one important wave parameter: its direction of arrival (DOA). Two important issues about the receiving antenna signals are addressed here: the effective length of the dipoles, and the computational method of determining the DOA from the amplitudes and relative phase of signals. The electric field radiated by the monopole elements composing the dipoles has been calculated using the NEC4 code. With recourse to the reciprocity principle that the effective length of the active dipole equals that of the same dipole as a receiving antenna, the dependence of the effective length on DOA has been computed, for various antenna-spacecraft configurations. For 3 m monopoles combined as dipoles, and for frequencies between 5 and 18 MHz, effective lengths can be well approximated using a simple expression for a short dipole, with modest adjustment to include asymmetries of the transmitting members. The radiation-reception patterns of isolated monopoles are quite symmetric, implying that the experiment does not depend critically on dipole signals. The antenna models provide a basis for the numerical technique for inverting the amplitude and phase of voltages induced by an plane wave incident on crossed dipoles to the DOA of the wave. The procedure assumes a cw elliptically polarized wave, taking account of plasma effects. The mathematics leads to expressions for the induced dipole voltages as functions of the wave vector azimuthal and polar angles. The inverse determination of the DOA angles is underspecified for only two dipoles, and requires selecting the true solution from two or more possible azimuth-polar pairs throughout the 4π sr solid-angle space surrounding the spacecraft. The selection of the solution will be guided by values expected for the known ground-transmitter and satellite positions, and by other wave parameter measurements.
Investigation of superparamagnetism in Co–Zn ferrite thin films produced by pulsed-laser deposition
Authors: Ravinder D. , Shalini P.
Published: June 2003

Modern communication systems use increasingly higher frequencies and smaller and lighter possible devices. This requires magnetic devices using thin-film inductors or transformers and microwave integrated nonreciprocal circuits with incorporated thin ferrite films. Due to their better high-frequency characteristics, the polycrystalline materials are preferred to the monocrystalline ones in such thin-film applications.
Contactless electroreflectance, in the range of 20 K<T<300 K, of freestanding wurtzite GaN prepared by hydride-vapor-phase epitaxy
Authors: Huang Y. S. , Pollak Fred H. , Park S. S. , Lee K. Y. , Morkoç H.
Published: June 2003

We have performed a detailed contactless electroreflectance study of the interband excitonic transitions on both the Ga and N faces of a 200-μm-thick freestanding hydride-vapor-phase-epitaxy grown wurtzite GaN sample with low defect concentration in the temperature range between 20 and 300 K. The transition energies of the A, B, and C excitons and broadening parameters of the A and B excitons have been determined by least-square fits to the first derivative of a Lorentzian line shape. The energy positions and separations of the excitonic transitions in the sample reveal the existence of residual strain. At 20 K the broadening parameter of A exciton deduced for the Ga (5×105 dislocation cm−2) and N (1×107 dislocation cm−2) faces are 3 and 7 meV, respectively, indicating a lower defect concentration on the former face. The parameters that describe the temperature dependence of the interband transition energies of the A, B, and C excitons as well as the broadening function of the A and B features are evaluated. The results from an analysis of the temperature dependence of the broadening function of excitons A and B indicate that GaN exhibits a very large exciton-phonon coupling.
Solid-phase crystallization behaviors of in situ phosphorous-doped amorphous silicon films deposited using Si2H6 and PH3
Authors: Yokoyama Shigeyuki , Onizuka Hisayuki , Yoshizawa Yuki , Kuwano Hiroshi
Published: June 2003

The solid-phase crystallization of in situ phosphorous-doped amorphous silicon films deposited by low-pressure chemical vapor deposition using disilane is studied for various P concentrations and annealing temperatures. The nucleation rate is found to follow a power law with respect to the annealing time. The power index is 1.3 for P concentrations up to about 5×1019 cm−3 and decreases slightly at higher P-doping levels. The grain growth rate is enhanced as the P concentration increases, particularly above 1×1019 cm−3. The activation energy of the grain growth rate is 2.6 eV regardless of the P concentration. The final grain size in the crystallized films increases markedly for a P concentration over 1×1019 cm−3, but is almost independent of the annealing temperature. The crystallization behavior and final grain size can be represented by equations extended from those of Avrami–Johnson–Mehl using the time-dependent nucleation rate.