bluuebunny/crossref_metadata_2025 huggingface dataset:
Techniques for measurement of thoracoabdominal asynchrony
Authors: Prisk G. Kim , Hammer J. , Newth Christopher J.L.
Published: November 2002

Respiratory motion measured by respiratory inductance plethysmography often deviates from the sinusoidal pattern assumed in the traditional Lissajous figure (loop) analysis used to determine thoraco‐abdominal asynchrony, or phase angle ϕ. We investigated six different time‐domain methods of measuring ϕ, using simulated data with sinusoidal and triangular waveforms, phase shifts of 0–135°, and 10% noise. The techniques were then used on data from 11 lightly anesthetized rhesus monkeys (Macaca mulatta; 7.6 ± 0.8 kg; 5.7 ± 0.5 years old), instrumented with a respiratory inductive plethysmograph, and subjected to increasing levels of inspiratory resistive loading ranging from 5–1,000 cmH2O · L−1 · sec−1.

The best results were obtained from cross‐correlation and maximum linear correlation, with errors less than ∼5° from the actual phase angle in the simulated data. The worst performance was produced by the loop analysis, which in some cases was in error by more than 30°. Compared to correlation, other analysis techniques performed at an intermediate level. Maximum linear correlation and cross‐correlation produced similar results on the data collected from monkeys (SD of the difference, 4.1°) but all other techniques had a high SD of the difference compared to the correlation techniques.

We conclude that phase angles are best measured using cross‐correlation or maximum linear correlation, techniques that are independent of waveform shape, and robust in the presence of noise. Pediatr Pulmonol. 2002; 34:462–472. © 2002 Wiley‐Liss, Inc.
Host brain regulation of dopaminergic grafts function: Role of the serotonergic and noradrenergic systems in amphetamine‐induced responses
Authors: Muñoz Ana , Rodriguez‐Pallares Jannette , Guerra Maria Jose , Labandeira‐Garcia Jose Luis
Published: November 2002

The indirect dopaminergic (DA) agonist amphetamine has frequently been used to study functional responses of DA grafted neurons. However, it is not known if striatal responses, primarily related to DA release by the grafted neurons, are modulated by the host striatal afferents. We investigated the changes in amphetamine‐induced rotational behavior and striatal expression of Fos in DA‐denervated and grafted rats subjected to serotonergic denervation and/or treatment with the α1‐adrenergic receptor antagonist Prazosin. Acute serotonergic lesions with p‐chlorophenylalanine suppressed the expression of Fos induced by 1 mg/kg of amphetamine in both the grafted and the contralateral striatum. Chronic serotonergic denervation with 5,7‐dihydroxytryptamine induced a significant reduction in Fos expression in both the grafted and nongrafted striata and a nonsignificant reduction in the contraversive rotation. In DA‐innervated striata, Prazosin significantly reduced the expression of Fos but only in the presence of serotonergic innervation. However, Prazosin did not decrease the expression of Fos induced by grafts located in striata not subjected to serotonergic denervation. The present results suggest functional integration of transplanted DA neurons and major host striatal afferent systems, particularly the serotonergic system, in modulating responses of the host striatal neurons. However, indirect effects exerted by the noradrenergic system on the normal striatum were not observed in the DA‐denervated and grafted striata. Synapse 47:66–76, 2003. © 2002 Wiley‐Liss, Inc.
Differences in regional and subcellular localization of Gq/11 and RGS4 protein levels in Alzheimer's disease: Correlation with muscarinic M1 receptor binding parameters
Authors: Muma Nancy A. , Mariyappa Ramesh , Williams Kyle , Lee John M.
Published: November 2002

Deficits in M1 muscarinic receptor system signaling in Alzheimer's disease (AD) prompted an analysis of components of these systems, namely, the Gq/11 protein and the regulator of G‐protein signaling (RGS) 4 protein. In AD parietal cortex, total levels of Gq/11 and RGS4 proteins were significantly lower than age‐matched control cases by 40% and 53%, respectively. However, the levels of membrane‐bound Gq/11 and RGS4 protein in AD parietal cortex were maintained at levels comparable to controls. Furthermore, in the frontal cortex and cerebellum both the total and membrane levels of Gq/11 and RGS4 protein were not altered in AD cases compared to control cases. To our knowledge, this is the first report to examine RGS proteins in AD. Using receptor binding assays on the parietal cortex membrane fractions from AD cases, we found the muscarinic agonist carbachol still bound to high‐ and low‐affinity sites (two‐site fit) and the potency of 5‐guanylylimidodiphosphate (GppNHp) to shift receptors from the high‐ to low‐affinity state (based on the ternary complex model) was greater in AD cases compared to controls. In contrast, we previously reported a lack of high‐affinity agonist binding sites in the frontal cortex in AD cases even in the absence of GppNHp. The data suggest that the equilibrium dynamics between the cytosolic and membrane levels of Gq/11 and RGS4 may contribute to the regional differences in the coupling of muscarinic M1 receptors in AD and have implications for the variability in effects of cholingeric treatment strategies currently in place. Synapse 47:58–65, 2003. © 2002 Wiley‐Liss, Inc.
‘It's Easier that you're a Girl and that you're Asian’: Interactions of ‘Race’ and Gender between Researchers and Participants
Authors: Archer Louise
Published: November 2002

This article is concerned with the ways in which ‘race’ and gender interact between interviewers and participants within the research process and the implications of differences/similarities between researcher and participants for feminist research and analysis. The paper discusses issues of power and representation within a research project conducted by the white female author and two Asian female interviewers with 64 British Muslim young men and women. Based on analysis of discussion group data, it is argued that ‘race’ and gender interact between researchers and participants in highly complex and unpredictable ways to produce particular accounts, but comparative analysis of accounts produced with different interviewers can help reveal ‘hidden’ structures of power within the texts.
‘First in Man’: The Politics and Ethics of Women in Clinical Drug Trials
Authors: Corrigan Oonagh P.
Published: November 2002

Within the world of pharmacology, the male body has traditionally been taken as the biological norm. Coupled with this, concern about danger to the unborn foetus has meant that, until very recently, ‘women of childbearing potential’ were routinely excluded from most of the early phases of clinical drug testing. Consequently, most drugs tested during Phase I trials were initially carried out on healthy male volunteers. During subsequent phases when drugs were tested on patients, women remained largely under-represented. As a result, some drugs prescribed for women have later been discovered to be lacking in efficacy, and women are more likely to suffer adverse drug reactions than men. The exclusion of women during the early phases of clinical drug trials has now been lifted and drugs are currently being more widely tested on women. This paper examines the differing political and ethical positions adopted by the pharmaceutical industry, drug regulators, pharmacologists, women's groups and patient activists in relation to the exclusion and inclusion of women in clinical drug trials.
Antiphase boundary network: A route to extract the island nucleation density
Authors: Zoethout E. , van den Hoogenhof P. W. , Zandvliet H. J. W. , Poelsema Bene
Published: November 2002

Epitaxial growth of Si or Ge on Si(001) and Ge(001) surfaces leads to the formation of an antiphase boundary network because adjacent (2×1) reconstructed islands can either be in-phase or out-of-phase with each other. We show that this antiphase boundary network can be used to extract the saturation island nucleation density well after the onset of coalescence. This method is more accurate than the commonly used method of counting the islands in the low coverage regime.
Detection of trap activation by ionizing radiation in SiO2 by spatially localized cathodoluminescence spectroscopy
Authors: White B. D. , Brillson L. J. , Bataiev M. , Brillson L. J. , Fleetwood D. M. , Schrimpf R. D. , Choi B. K. , Fleetwood D. M. , Pantelides S. T.
Published: November 2002

Microcathodoluminescence (CLS) spectroscopy is used to probe the effect of ionizing radiation on defects inside Al gate oxide structures. Micron-scale Al–SiO2–Si capacitors exposed to 10 keV x-ray irradiation exhibit spatially localized CLS emissions characteristic of multiple deep level traps, including positively charged oxygen-deficient centers and nonbridging oxygen hole centers (NBOHC). Irradiation produces both increases and decreases in their relative emission intensities, depending on spatial location within the oxide. These changes result in a gradient of E′ versus NBOHC defect densities across the oxide thickness between Al and Si interfaces. These results demonstrate that x-ray irradiation-induced deep level traps can be monitored spatially in metal-oxide-semiconductor gate structures, that x-ray irradiation produces separate increases or decreases in E′ versus NBOHC defect densities, and that these changes vary with position within the oxides.
Regression procedure for determining the dopant profile in semiconductors from scanning capacitance microscopy data
Authors: Marchiando J. F. , Kopanski J. J.
Published: November 2002

A regression procedure has been developed to correlate scanning capacitance microscope (SCM) data with dopant concentration in three dimensions. The inverse problem (calculation of the dopant profile from SCM data) is formulated in two dimensions as a regularized nonlinear least-squares optimization problem. For each iteration of the regression procedure, Poisson’s equation is numerically solved within the quasistatic approximation. For a given type model ion-implanted dopant profile, two cases are considered; the background doping is either the same or the opposite type as that ion-implanted. Due to the long-range nature of the interactions in the sample, the regression is done using two spatial meshes: a coarse mesh and a dense mesh. The coarse mesh stepsize is of the order of the probe-tip size. The dense mesh stepsize is a fraction of the coarse mesh stepsize. The regression starts and proceeds with the coarse mesh until the spatial wavelength of the error or noise in the estimated dopant density profile is of the order of the coarse mesh stepsize. The regression then proceeds in like manner with the dense mesh. Regularization and filtering are found to be important to the convergence of the regression procedure.
One- and two-phonon capture processes in quantum dots
Authors: Magnusdottir I. , Uskov A. V. , Bischoff S. , Tromborg B. , Mørk J.
Published: November 2002

Multiphonon capture processes are investigated theoretically and found to contribute efficiently to the carrier injection into quantum dots. It is shown that two-phonon capture contributes where single-phonon capture is energetically inhibited and can lead to electron capture times of a few picoseconds at room temperature and carrier densities of 1017 cm−3 in the barrier.
Model of laser-aided heating and evaporation of particles
Authors: Tiwari Pawan K. , Tripathi V. K.
Published: November 2002

The efficacy of an intense laser for dissolving metallic particles in material processing plasmas has been examined. The laser penetrates in the skin layer of the particles and heats them. The temperature rise of the particle is, however, uniform due to the predominance of thermal conduction. As the particle temperature rises heating rate increases due to increase in electron-phonon collisional frequency. Once the transition to liquid phase occurs the conductivity falls drastically slowing the heating rate. However, in the vapor phase ionization begins and the plasma thus formed expands at the velocity of sound while simultaneously absorbing energy from the tail of the laser pulse.
Analytical method for finding the general optical properties of semiconductor deep centers
Authors: Pan Janet L.
Published: November 2002

The optical properties of deep centers and their dependence on general materials parameters are predicted from an analytical eight-band k⋅p model of deep-center states. A wide variety of deep centers in a wide variety of direct-gap semiconductors can be modeled this way. Scanning-tunneling-microscopy images and measured optical dipoles are in excellent agreement with our model. Our model of deep-center optical properties is the most detailed, multiband k⋅p model which remains fully analytical. Our model of deep centers goes beyond previous work in being able to simultaneously explain, within an analytical framework, both the size and spectral shape of the experimentally measured cross sections for optical transitions from deep levels to (i) the valence band, and (ii) the conduction band; as well as, (iii) observed optical selection rules, and (iv) scanning-tunneling-microscopy images of deep-level bound states. Very good agreement is observed between our model and experiment for deep levels in a variety of (large and small band-gap) semiconductors: the arsenic antisite in both GaAs and In0.53Ga0.47As; the chromium substitutional impurity in both GaAs and InP; and the indium vacancy in InSb. Good agreement is achieved between our model and experiment because both the size and spectral shape of the cross sections for direct optical transitions from the deep level (to the conduction or valence-band edge) is found to be determined by the small-wave-vector component of the deep-center wave function. It is precisely the small-wave-vector component of the deep-center wave function which is described well by our eight-band k⋅p model. Significantly, this agreement between our model and experiment is a vindication of the general materials parameters (Kane dipole, nonparabolic effective masses, band-gap energy, spin-orbit splitting) characterizing our eight-band model of deep centers, rather than a result of careful use of adjustable parameters. Our model shows that the spatial extent of the deep-center bound state is proportional to the Kane dipole, and is thus larger (more delocalized) in a smaller band-gap semiconductor. Moreover, our model shows that, in order to successfully predict optical properties, a linear combination of atomic orbitals describing deep centers must extend over many lattice sites: more than just the neighbors and next-nearest neighbors of the deep center.
Experimental verification of backward-wave radiation from a negative refractive index metamaterial
Authors: Grbic Anthony , Eleftheriades George V.
Published: November 2002

A composite medium consisting of an array of fine wires and split-ring resonators has been previously used to experimentally verify a negative index of refraction. We present a negative refractive index (NRI) metamaterial that goes beyond the original split-ring resonator/wire medium and is capable of supporting a backward cone of radiation. We report experimental results at microwave frequencies that demonstrate backward-wave radiation from a NRI metamaterial—a characteristic analogous to reversed Cherenkov radiation. The conception of this metamaterial is based on a fresh perspective regarding the operation of NRI metamaterials.
Impact of nucleation conditions on the structural and optical properties of M-plane GaN(11̄00) grown on γ-LiAlO2
Authors: Sun Yue Jun , Brandt Oliver , Jahn Uwe , Liu Tian Yu , Trampert Achim , Cronenberg Sven , Dhar Subhabrata , Ploog Klaus H.
Published: November 2002

We investigate the structural and optical properties of M-plane GaN(11̄00) films grown on LiAlO2(100) with nucleation layers grown at high and low temperatures. Samples with a high temperature nucleation layer are found to exhibit a highly anisotropic surface morphology with pronounced corrugation, which basically replicates the surface morphology of the substrate. Photoluminescence spectra of these layers are dominated by a transition at 3.356 eV, which is absent for samples with a low-temperature nucleation layer. In conjunction with scanning electron microscopy, cathodoluminescence maps reveal that this transition predominantly stems from regions below the trenches of the surface corrugation. Transmission electron microscopy shows an abundance of stacking faults within these regions. Excitation-dependent and time-resolved photoluminescence demonstrates the intrinsic character of the 3.356 eV emission, which is thus attributed to excitons bound to stacking faults acting as ultrathin vertical quantum wells in these samples. Low-temperature nucleation is imperative to avoid thermal roughening of the substrate and thus the formation of a high density of stacking faults.
Investigation of grain formation and growth in nickel-induced lateral crystallization process
Authors: Yuen C. Y. , Poon M. C. , Chan W. Y. , Qin M.
Published: November 2002

In this article a simple method to reveal the direction of grain growth in nickel-induced lateral crystallization (NILC) is demonstrated. This method uses 6000 Å amorphous silicon film as the starting layer which is then crystallized by nickel. Then silicon dry etching is used to delineate the grains and the condition of grain growth in NILC is clearly shown. It is found that the grain growth directionality and uniformity are greatly dependent on the relative position and the shape of the nickel source origin. The optical microscope shows that the grain formation is in triangular shape. The structural condition is confirmed by an atomic force microscope which is used to scan over the grain. A mechanism of grain growth related to the movement of nickel silicide chains is proposed. Performances of n-channel metal–oxide–semiconductor transistors fabricated on different positions of the crystallized region are compared and it is found that the grain growth directionality shown after this grain-revealing method has a high correlation with the quality of the silicon in that region.
Dynamics of CO elimination from reactions of yttrium atoms with formaldehyde, acetaldehyde, and acetone
Authors: Schroden Jonathan J. , Teo Maurice , Davis H. Floyd
Published: November 2002

Reactions of neutral, ground-state yttrium atoms with formaldehyde, acetaldehyde, and acetone (Y+RR′CO, where R,R′=H,CH3) were studied in crossed molecular beams. At collision energies greater than 24 kcal/mol, four product channels were observed corresponding to elimination of CO, H2, H, and nonreactive scattering. For the dominant CO elimination channel, a large fraction (34%–41%) of the available energy appeared as kinetic energy of the products. RRKM modeling indicated this was a result of two factors: a large potential energy barrier for R′ migration leading to (R)(R′)YCO and dissociation of this complex prior to complete energy randomization. The CM angular distributions were all forward–backward symmetric, indicating the existence of at least one long-lived reaction intermediate. The angular distributions ranged from being quite forward–backward peaking for the Y+H2CO reaction to isotropic for Y+(CH3)2CO. A simple equation is derived based on statistical complex theory that relates the shape of the CM angular distributions to the structure of the dissociating complex.
Effects of buffer layer thickness and strain on the dielectric properties of epitaxial SrTiO3 thin films
Authors: James A. R. , Xi X. X.
Published: November 2002

The dielectric behavior of SrTiO3 (STO) thin films grown epitaxially on different substrates using pulsed laser ablation is reported in this article. The thickness of the SrRuO3 buffer layer, serving as an electrode, was varied from 500 to 5000 Å, to study the dependence of dielectric properties of the STO films on the buffer layer thickness. Strains introduced during the high-temperature deposition of these films, seem to greatly influence the dielectric behavior observed in them in the form of loss peaks. This article also reports the results of tunability and the results of dielectric measurements are correlated to the strain in the films.
Knudsen forces on microcantilevers
Authors: Passian A. , Wig A. , Meriaudeau F. , Ferrell T. L. , Thundat T.
Published: November 2002

When two surfaces at two different temperatures are separated by a distance comparable to a mean-free path of the molecules of the ambient medium, the surfaces experience Knudsen force. This mechanical force can be important in microelectromechanical systems and in atomic force microscopy. A theoretical discussion of the magnitude of the forces and the conditions where they can be encountered is discussed. A potential application of the Knudsen force in designing a cantilever-based vacuum gauge is discussed.
Evaluation of electro-optic, elasto-optic, piezoelectric, and elastic coefficients of Ba0.77Ca0.23TiO3 through orientation dependent photorefractive beam coupling
Authors: Bernhardt Sylvie , Mize Lauren , Delaye Philippe , Roosen Gérald
Published: November 2002

We present a demonstration of the influence of the indirect electro-optic effect on the photorefractive performance of Ba0.77Ca0.23TiO3 (BCT). The comparison of the orientation dependence of the two-beam coupling energy transfer gain with theoretical model allows us to obtain information on the electro-optic coefficients, but also an evaluation of the unknown elasto-optic, piezoelectric, and elastic stiffness coefficients of BCT. We found r13T=33 pm V−1 and r33T=170 pm V−1. These values are in good agreement with other published values. For the interesting coefficient r42T, we find a higher value r42T=465 pm V−1 than the one previously published. From this study we also determine that as in the case of BaTiO3, the optimal orientation is given by a 45°-cut BCT.
Integral encounter theories of multistage reactions. IV. Account of internal quantum states of reactants
Authors: Ivanov K. L. , Lukzen N. N. , Morozov V. A. , Doktorov A. B.
Published: November 2002

The matrix-form kinetic formalism developed earlier for multistage chemical reactions is generalized to the case of reactants with internal quantum quasiresonant states. Such internal quantum states may arise due to spins of the unpaired electrons of radicals or nuclear spins. The formalism gives an infinite hierarchy for matrix correlation patterns that can be truncated in two different ways. The simplest one reproduces the conventional integral encounter theory (IET). The second way results in the generalized modified encounter theory (MET). In the spinless problems such as intermolecular energy transfer MET is known to improve the results obtained with other methods. Thus we believe that the generalized MET taking account of all binary contributions will have wider applicability range than the conventional IET.
Spontaneous formation of stacking faults in highly doped 4H–SiC during annealing
Authors: Kuhr Thomas A. , Liu JinQiang , Chung Hun Jae , Skowronski Marek , Szmulowicz Frank
Published: November 2002

4H–SiC samples doped with nitrogen at ∼3×1019 cm−3 were annealed in Ar for 90 min at 1150 °C. Transmission electron microscopy revealed stacking faults at a density of approximately 80 μm−1 where faults were not found to exist prior to annealing. All faults examined were double layer Shockley faults formed by shear on two neighboring basal planes. The structural transformation was interpreted as due to quantum well action, a mechanism where electrons in highly n-type 4H–SiC enter stacking fault-induced quantum well states to lower the system energy. The net energy gain was calculated as a function of temperature and nitrogen doping concentration through solution of the charge neutrality equation. Calculations showed that doping levels in excess of ∼3×1019 cm−3 should result in double layer stacking faults forming spontaneously at device processing temperatures, in agreement with our observations. Single layer faults are not expected to be stable in 4H–SiC at concentrations below 1×1020 cm−3, but are expected to form at doping concentrations above ∼2×1019 cm−3 in 6H–SiC. Charge buildup in the stacking fault was shown to produce an electrostatic potential that exceeds 90% of the energy difference between the Fermi level position and lowest energy state in the fault-related quantum well. This potential barrier is one of the factors leading to increase of the forward voltage drop in SiC pin diodes.
Raman spectroscopy and photoluminescence of ZnTe thin films grown on GaAs
Authors: Camacho J. , Cantarero A. , Hernández-Calderón I. , González L.
Published: November 2002

We report resonant Raman scattering and photoluminescence (PL) measurements on two ZnTe thin films grown by molecular-beam epitaxy on GaAs substrates with thicknesses around 0.5 and 1.0 μm. The data have been obtained by using the different excitation energies of an Ar+ laser to distinguish Raman from PL and analyze resonant effects. The characteristic features of the low-temperature PL spectra are the light and heavy free exciton emissions, split due to the thermal strain effect, followed by several phonon replicas of these lines. Moreover, longitudinal and transversal polariton splittings of heavy excitons are clearly observed. Their reduced masses have been obtained from the exciton binding energies. Room and low-temperature Raman spectra show, besides the typical longitudinal optical (LO) multiphonon emissions, forbidden zone-center transverse optical (TO)+(n−1)LO phonon combinations, which yield an accurate value for the LO and TO phonon energies. The breakdown of the selection rules is attributed to surface faceting.
Thermal annealing of Si/SiO2 materials: Modification of structural and photoluminescence emission properties
Authors: Khriachtchev Leonid , Novikov Sergei , Lahtinen Jouko
Published: November 2002

We comparatively study two conventional types of Si/SiO2 materials, Si/SiO2 superlattices (SLs) and Si-rich silica (SiOx) films, prepared with a molecular beam deposition method. Raman scattering, photoluminescence (PL), ultraviolet-visible-infrared absorption, and x-ray photoelectron spectroscopies are employed to characterize the samples. The results show clear parallelism in microstructure and emitting properties of Si/SiO2 SLs and SiOx films. The as-grown material is amorphous, and disordered Si areas are seen in Raman spectra for samples with higher Si contents. Annealing at 1150 °C in nitrogen atmosphere leads to ordering of the Si grains and the typical crystalline size is estimated to be 3–4 nm. For all samples, an annealing-induced increase of PL at ∼1.6 eV is observed, and its resulting position is quite independent of the initial sample architecture. Furthermore, this PL is practically identical for continuous wave and pulsed excitation at 488 nm as well as for pulsed excitation at various wavelengths (266–488 nm), and the order of PL lifetimes is 1–10 μs. No correlation between the crystallite concentration and the PL intensity for the annealed samples is found, and the strongest PL was obtained for two samples with less defined crystallization. The origin of the annealing-induced 1.6 eV PL band is discussed.
Determination of the structures of distinct transition state ensembles for a β-sheet peptide with parallel folding pathways
Authors: Davis Rayhan , Dobson Christopher M. , Vendruscolo Michele
Published: November 2002

The occurrence of well defined multiple folding pathways, although possible in principle, is rarely observed experimentally in small globular proteins. In molecular dynamics simulations, however, β3s, a synthetic 20 residue peptide, folds along two alternative pathways into a monomeric β-sheet structure. The structures of the corresponding transition states for folding have been defined in these simulations [Ferrara and Caflisch, PNAS 97, 10780 (2000)]. We describe a method for the simultaneous back-calculation of the two transition state structures of β3s from the knowledge of the average number of native contacts formed by individual residues. The structures are determined by a Monte Carlo approach in which two replicas of the peptide are simulated in parallel. This procedure generalizes one that we have recently developed to determine transition state structures from experimental φ values. Our results show that, while the short peptide β3s has two folding pathways, the 98 residue protein AcP folds via a single pathway. We conclude by discussing how evolution may have selected single folding pathways as a “quality control” mechanism to avoid misfolding.
Use of multiple-edge refinement of extended x-ray absorption fine structure to determine site occupancy in mixed ferrite nanoparticles
Authors: Calvin S. , Carpenter E. E. , Harris V. G. , Morrison S. A.
Published: November 2002

The site occupancy of manganese zinc ferrite (MZFO) nanoparticles is determined by a multiple-edge refinement of the extended x-ray absorption fine structure of the manganese, zinc, and iron absorption edges. The MZFO nanoparticles are generated by a reverse micellar synthetic route and compared to a ceramic standard. The simultaneous fitting of multiple absorption edges to a constrained model is found to yield site occupancies accurate to within eight percentage points.
Microstructure evolution and abnormal grain growth during copper wafer bonding
Authors: Chen K. N. , Fan A. , Tan C. S. , Reif R. , Wen C. Y.
Published: November 2002

Evolution of microstructure morphologies and grain orientations of Cu–Cu bonded wafers during bonding and annealing were studied by means of transmission electron microscopy, electron diffraction, and x-ray diffraction. The bonded Cu grain structure reaches steady state after post-bonding anneal. An abnormal (220) grain growth was observed during the initial bonding process. Upon annealing, the preferred grain orientation of the whole film shifts from (111) to (220). The effects of yielding and energy minimization are possible reasons for the evolution of the preferred grain orientation.
A three-phase magnetoelectric composite of piezoelectric ceramics, rare-earth iron alloys, and polymer
Authors: Nan C.-W. , Liu L. , Cai N. , Zhai J. , Ye Y. , Lin Y. H. , Dong L. J. , Xiong C. X.
Published: November 2002

A class of multiferroic, three-phase particulate composites of Tb–Dy–Fe alloy, lead–zirconate–titanate (PZT), and polymer are investigated, in which a small volume fraction f of Tb–Dy–Fe alloy particles are dispersed in a PZT/polymer mixture. The measured dielectric, piezoelectric, and magnetoelectric properties demonstrate that a percolation transition occurs at f∼0.12 in the composites. When f is low (e.g., f<0.07), the composites exhibit piezoelectric and increasing magnetoelectric response. In the critical f range of 0.07<f<0.12, such piezo- and magnetoelectric responses sharply drop, and equal zero at the percolation threshold, above which the composite becomes a conductor and a magnetostrictive composite only.
Structural characteristics and magnetic properties of chemically synthesized CoPt nanoparticles
Authors: Yu Andrew C. C. , Mizuno M. , Sasaki Y. , Kondo H. , Hiraga K.
Published: November 2002

Co x Pt 100−x nanoparticles with dimensions from approximately 2 to 5 nm were synthesized using the reverse micelle method. High-resolution electron microscopy revealed single- and poly-crystalline nanoparticle structures. Twin boundary is a common feature in the polycrystals. As-grown nanoparticles did not show any coercivity at room temperature. However, the nanoparticles became ferromagnetic after annealing at 550 °C for 4 h. Face-centered-cubic to face-centered-tetragonal phase transformation of the nanoparticles that occurred at annealing temperatures above 550 °C was confirmed by electron diffraction patterns and x-ray diffractometry. Coercivity of the annealed nanoparticles were found depending on the nanoparticle chemical compositions. Composition atomic ratio of Co to Pt at around unity gives the highest coercivity of 5500 Oe at room temperature.
Sum frequency generation of synchronously-seeded, high-power Yb and Er fiber amplifiers in periodically poled KTP
Authors: Champert P. A. , Popov S. V. , Avdokhin A. V. , Taylor J. R.
Published: November 2002

Synchronous temporal seeding of single-mode, high-peak, and average-power Yb and Er fiber amplifiers allowed efficient, single-pass, sum frequency generation in periodically poled KTP. 3.5 W average power in the red, at 630 nm, is generated with Gaussian spatial beam quality.
Detachment of nanotubes from a polymer matrix
Authors: Cooper Carole A. , Cohen Sidney R. , Barber Asa H. , Wagner H. Daniel
Published: November 2002

A technique to investigate the adhesion of carbon nanotubes to a polymer matrix is described. Carbon nanotubes bridging across holes in an epoxy matrix have been drawn out using the tip of a scanning probe microscope while recording the forces involved. A full force-displacement trace could be recorded and correlated with transmission electron micrographs observations prior and subsequent to the tip action. Based on these experiments, an approximate calculation of the nanotube-polymer interfacial shear strength has been performed.
Thermomechanical Buckling of Laminated Composite Plates Using Mixed, Higher-Order Analytical Formulation
Authors: Dafedar J. B. , Desai Y. M.
Published: November 2002

A novel, analytical mixed theory based on the potential energy principle has been presented in this paper to investigate buckling response of laminated composite plates subjected to mechanical and hygrothermal loads. Two sets of higher-order mixed models have been proposed on the basis of an individual layer as well as equivalent single layer theories by selectively incorporating nonlinear components of Green’s strain tensor. Displacements, as well as transverse stress continuities, have been enforced in the formulation of models by incorporating displacements and transverse stresses as the degrees-of-freedom. The modal transverse stresses have been obtained as eigenvectors and thus their separate calculations have been advantageously avoided. Solutions from the models have been shown to be in excellent agreement with the available three-dimensional elasticity solutions. Few benchmark solutions have also been presented for the bi-axial compression-tension loading.
Motorcycle Steering Oscillations due to Road Profiling
Authors: Limebeer D. J. N. , Sharp R. S. , Evangelou S.
Published: November 2002

A study of the effects of regular road undulations on the dynamics of a cornering motorcycle is presented. This work is based on an enhanced version of the motorcycle model described in “A Motorcycle Model for Stability and Control Analysis” (R. S. Sharp and D. J. N. Limebeer, 2001, Multibody Syst. Dyn., Vol. 6, No. 2, pp. 123–142). We make use of root-locus and frequency response plots that were derived from a linearized version of this model; the linearization is for small perturbations from a general steady-cornering equilibrium state. The root-locus plots provide information about the damping and resonant frequencies of the key motorcycle modes at different machine speeds, while the frequency response plots are used to study the propagation of road forcing signals to the motorcycle steering system. Our results are based on the assumption that there is road forcing associated with both wheels and that there is a time delay between the front and rear wheel forcing signals—this is sometimes referred to as wheelbase filtering. As has been explained before, control systems are used in the nonlinear simulation code to establish and maintain the machine’s speed and roll angle at preset values (for flat road running). These controllers are used to find the machine’s equilibrium state and not to emulate a rider’s control actions. The results show that at various critical cornering conditions, regular road undulations of a particular wavelength can cause severe steering oscillations. At low speeds the machine is susceptible to road forcing signals that excite the lightly damped wobble and front suspension pitch modes. At higher speeds it is the weave and front wheel hop modes that become vulnerable to road forcing. We believe that the results and theory presented here explain many of the stability related road accidents that have been reported in the popular literature and are therefore of practical import. The models used in this research make use of the multibody modelling package AUTOSIM (Autosim 2.5+ Reference Manual, 1998, Mechanical Simulation Corporation) and are available at the web site http://www.ee.ic.ac.uk/control/motorcycles/. The motorcycle and tire parameters can be found at the end of the code.
High-sensitivity x-ray photoelectron spectroscopy characterization of a quantum device structure
Authors: Wintrebert-Fouquet M. , Butcher K. S. A.
Published: November 2002

A high-resolution, high-sensitivity VG x-ray photoelectron spectrometer was used to study a semiconductor layer structure grown for the fabrication of resonant tunneling bipolar transistor devices. Depth profiling using argon ion milling, at a rate of 50 Å/min, has allowed the device layers to be identified on the basis of their elemental composition. The measurement system sensitivity was sufficient to identify the elemental components of the 11 Å AlAs barrier layer in quantum tunneling InGaAs/AlAs device layers.
Microstructure and properties of Ti–Si–N nanocomposite films
Authors: Hu Xiaoping , Han Zenghu , Li Geyang , Gu Mingyuan
Published: November 2002

Ti–Si–N nanocomposite films were deposited by multitarget reactive magnetron sputtering. Energy dispersive spectroscopy, X-ray diffraction, transmission electron microscopy, and x-ray photoelectron spectroscopy were employed to characterize their microstructure and a microhardness tester was used to measure their hardness. The influence of substrate temperature on these films was investigated, too. The results reveal that the films consist of TiN and Si3N4. Si3N4 exists as amorphous, which strongly prevents the growth of TiN grains and causes TiN to form a nanocrystalline or amorphous phase. The hardness of films deposited at room temperature reaches the peak value of 36 GPa at a Si content of 4.14 at. %, and then decreases gradually with the increase of Si content. The enhancement of the substrate temperature weakens the restraint effect of amorphous Si3N4 on the growth of TiN grains, which results in coarse TiN grains and subsequently leads to a lower peak value and a slower decrease of the hardness of the films.
Plasma polymerization and deposition of linear, cyclic and aromatic fluorocarbons on (100)-oriented single crystal silicon substrates
Authors: Yang G. H. , Oh S. W. , Kang E. T. , Neoh K. G.
Published: November 2002

Fluoropolymer films were deposited on the Ar plasma-pretreated Si(100) surfaces by plasma polymerization of perfluorohexane (PFH, a linear fluorocarbon), perfluoro(methylcyclohexane) (MCH, a cyclic fluorocarbon), and hexafluorobenzene (HFB, an aromatic fluorocarbon) under different glow discharge conditions. The effects of the radio-frequency plasma power on the chemical composition and structure of the plasma-polymerized fluoropolymer films were studied by x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, time-of-flight secondary ion mass spectrometry, and water contact angle measurements. The changes in structure and composition of the three types of the plasma-deposited films from those of the respective fluorocarbons were compared. Under similar glow discharge conditions: (i) the extent of defluorination was highest for the PFH polymer, (ii) the deposition rate was highest for the HFB polymer, (iii) the cyclic structure of MCH was less well preserved than the aromatic structure of HFB, (iv) aliphatic structures appeared in the plasma-deposited MCH polymer, and (v) the plasma-polymerized HFB has the highest thermal stability due to the preservation of the aromatic rings. The adhesive tape peel test results revealed that the plasma-polymerized and deposited fluoropolymer layers were strongly bonded to the Ar plasma-pretreated Si(100) surfaces.
A novel silicon array designed for intraoperative charged particle imaging
Authors: Tornai Martin P. , Patt Bradley E. , Iwanczyk Jan S. , Tull Carolyn R. , MacDonald Lawrence R. , Hoffman Edward J.
Published: November 2002

A novel Si‐PIN imaging array is under investigation for a charged particle (beta, positron, or alpha) sensitive intraoperative camera to be used for (residual) tumor identification during surgery. This class of collimator‐less nuclear imaging device has a higher signal response for direct interactions than its scintillator‐optical detector‐based counterparts. Monte Carlo simulations with 635 keV betas were performed, yielding maximum and projected ranges of 1.64 and 0.55 mm in Si. Up to 90% of these betas were completely absorbed in the first 0.30 mm. Based on these results, 300 μm thick prototype Si detector arrays were designed in a 16×16 crossed‐grid arrangement with 0.8 mm wide orthogonal strips on 1.0 mm pitch. A NIM‐ and CAMAC‐based high‐density data acquisition and processing system was used to collect the list mode data. The system was calibrated by comparisons of measured spectra to energy deposition simulations or by direct measurement of various >100 keV conversion electron or beta emitters. Mean electronic noise per strip was <3.6 keV FWHM at room temperature. When detecting positrons, which have an accompanying 511 keV annihilation background, the flood irradiated beta/gamma ratio was ∼40, indicating that beta images could be made without the use of background rejection techniques. The intrinsic spatial resolution corresponds to the 1×1pixel size, and measurements of beta emitting point and line sources yielded FWHM resolutions of 1.5 (lateral) and 2.5 mm (diagonal), respectively, with the larger widths due to particle range blurring effects. Deconvolution of the finite source size yielded intrinsic resolutions that corresponded to the image pixel size. Transmission images of circle and line phantoms with various hole sizes and pitch were resolved with either pure beta or positron irradiation without a background correction. This novel semiconductor imaging device facilitates high charged particle and low gamma sensitivity, high signal/noise ratio, and allows for compact design to potentially aid surgical guidance by providingin situimages of clinical relevance.
Evaluation and characterization of parallel plate microchamber's functionalities in small beam dosimetry
Authors: Lee Heung‐Rae , Pankuch Mike , Chu James C. , Spokas John J.
Published: November 2002

A parallel plate microchamber (PPMC) has been designed to specifically address the problems of small beam dosimetry. The chamber's extremely small volume and tissue equivalency theoretically make it possible for the chamber to perform an ideal measurement for small field dosimetry. Results show the PPMC to be a simple and reproducible detector for the measurements of total scattering factors, percentage depth doses, and off‐axis ratios. Even with its unique geometry, the PPMC requires a correction factor when measuring total scatter factors of fields smaller than 2.5 cm in diameter. Results obtained with the PPMC for fields greater than 2.5 cm diameter closely match those of alternative measurement modalities. The exceptionally small volume of the chamber increases the effect of radiation‐induced cable currents. With careful experimental technique, this problem can be resolved. Monte Carlo simulations of a Sun Nuclear QED low build‐up diode were done to show that no correction factor is needed for the diode in measuring total scatter factors of small fields. However, the scattering factors measured with the PPMC should be corrected for cone fields smaller than 2.5 cm in diameter. With the correction factor, the scattering factor obtained with the PPMC matches that with the QED diode within 0.7%. The percent depth dose data taken with the PPMC for a 40×40field closely matches that taken with the PTW chamber with the largest deviation being ∼1.2% at a depth of 30 cm. For a measurement of the off‐axis ratio with stereotactic cones of diameter 1.25 and 4.0 cm, the data obtained with the PPMC have a good agreement (less than 0.5% difference) with the film measurement.
An evaluation of gating window size, delivery method, and composite field dosimetry of respiratory‐gated IMRT
Authors: Hugo Geoffrey D. , Agazaryan Nzhde , Solberg Timothy D.
Published: November 2002

A respiratory gating system has been developed based on a commercial patient positioning system. The purpose of this study is to investigate the ability of the gating system to reproduce normal, nongated IMRT operation and to quantify the errors produced by delivering a nongated IMRT treatment onto a moving target. A moving phantom capable of simultaneous two‐dimensional motion was built, and an analytical liver motion function was used to drive the phantom. Studies were performed to assess the effect of gating window size and choice of delivery method (segmented and dynamic multileaf collimation). Additionally, two multiple field IMRT cases were delivered to quantify the error in gated and nongated IMRT with motion. Dosimetric error between nonmoving and moving deliveries is related to gating window size. By reducing the window size, the error can be reduced. Delivery error can be reduced for both dynamic and segmented delivery with gating. For the implementation of dynamic IMRT delivery in this study, dynamic delivery was found to generate larger delivery errors than segmented delivery in most cases studied. For multiple field IMRT delivery, the largest errors were generated in regions where high field modulation was present parallel to the axis of motion. Gating was found to reduce these large errors to clinically acceptable levels.
Normalized conceptus doses for abdominal radiographic examinations calculated using a Monte Carlo technique
Authors: Damilakis John , Tzedakis Antonis , Sideri Liana , Perisinakis Kostas , Stamatelatos Ion E. , Gourtsoyiannis Nicholas
Published: November 2002

The aim of the present study was to develop a reliable method for estimating conceptus radiation doses resulting from abdominal radiographic examinations for all trimesters of pregnancy. The method is based on normalized conceptus doses estimated using Monte Carlo modeling. The Monte Carlo N‐Particle (MCNP) radiation transport code was employed in the current study. The validity of the MCNP computational approach was verified by comparison with dose data obtained in anthropomorphic phantoms simulating pregnancy at the three trimesters of gestation using thermoluminescence dosimetry (TLD). The results consist of radiation doses normalized to air kerma so that conceptus dose from any technique and x‐ray unit used for abdominal radiography can be easily calculated. Normalized conceptus doses are presented for the first, second, and third trimesters of gestation for various kVp and total beam filtration values. Data apply to radiographic systems equipped with high frequency or 3 phase 12 pulse generators. A very good agreement was observed between the normalized conceptus doses estimated by TLD measurements and the MCNP simulation for all periods of gestation (maximum difference 8.1%). The results of MCNP procedures were compared to published data obtained by TLD measurements. Normalized conceptus dose values agree well, with most differences being lower than 10%. The normalized doses obtained in the current study are dependent on field size. However, for small changes in the size of the x‐ray field, the change in normalized doses is not considerable. Accurate estimation of conceptus doses due to abdominal conventional x‐ray examinations can be made using the dose data provided in the current study.