bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation of pacemaker frequency in the murine gastric antrum
Authors: Kim Tae Wan , Beckett Elizabeth A. H. , Hanna Rhonda , Koh Sang Don , Ördög Tamás , Ward Sean M. , Sanders Kenton M.
Published: July 2002

PGE2 has been linked to the production of gastric arrhythmias such as tachygastria. The interstitial cells of Cajal (ICC) generate electrical rhythmicity in gastrointestinal muscles, and may therefore be a target for PGE2 in gastric muscles. We cultured ICC from the murine gastric antrum, verified that cells were Kit immunoreactive, and measured spontaneous slow waves. These events were caused by spontaneous inward (pacemaker) currents that were not blocked by nifedipine. Forskolin and 8‐bromoadenosine 3′:5′‐cyclic monophosphate (8‐Br‐cAMP) reduced the frequency of pacemaker currents in ICC and of slow waves in intact antral muscles. The effects of forskolin and 8‐Br‐cAMP were not blocked by inhibitors of protein kinase A, suggesting that cAMP has direct effects on pacemaker activity. PGE2 mimicked the effects of forskolin and 8‐Br‐cAMP on ICC, but increased slow‐wave frequency in intact muscles. Therefore, the chronotropic effects of specific prostaglandin EP receptor agonists were examined. Butaprost and ONO‐AE1‐329, EP2 and EP4 receptor agonists, mimicked the effects of forskolin and 8‐Br‐cAMP on ICC and intact muscles. Sulprostone (EP3>EP1 agonist), GR63799, and ONO‐AE‐248 (EP3 agonists) enhanced the frequencies of pacemaker currents in ICC and slow waves in intact muscles. The effects of sulprostone were not blocked by SC‐19220, an EP1 receptor antagonist. These observations suggest that the positive chronotropic effects of PGE2 in intact muscles are mediated by EP3 receptor stimulation. The effects of PGE2 in intact muscles may be dependent upon the relative expression of EP receptors and/or proximity of receptors to sources of PGE2.
Three Stages of Fatigue Crack Growth in GFRP Composite Laminates
Authors: Tong Jie
Published: July 2002

Multiple fatigue crack growth behavior has been studied in model transparent GFRP laminates. Detailed experimental observations have been made on the growth of individual fatigue cracks and on the evolution of cracks in off-axis layers in 0/90/±45S and ±45/90S laminates. Three stages of fatigue crack growth in the laminates have been identified: initiation, steady-state crack growth (SSCG), crack interaction and saturation. The results show that SSCG rate is essentially constant under constant load, independent of crack length and crack spacing. Finite element models have been developed and used to calculate the strain energy release rates associated with the off-axis matrix cracking. A correlation has been achieved between fatigue crack growth rates in off-axis layers and the total strain energy release rates.
Reductions in Acquisition Costs for State-of-the-Art Fabrication of CFCC Turbine Engine Combustor Liners
Authors: Craig Phillip A. , Godfrey David
Published: July 2002

Through work in two U.S. Department of Energy cooperative programs with industry, the confidence level for utilization of ceramic composite SiC/SiC combustor liners has risen from a prototype curiosity to serious planning and addressing of hurdles for commercialization. One of the most significant hurdles for true commercialization is affordability of the ceramic composite combustor liners. To study the manufacturing costs for CFCC liners, a study was conducted to identify cost items and relationships. This report describes the effort, identifies the high impact areas of manufacturing costs, and recommends potential approaches to reducing the manufacturing costs. [S0742-4795(00)02703-4]
Use of k−ε−γ Model to Predict Intermittency in Turbulent Boundary-Layers
Authors: Dewan Anupam , Arakeri Jaywant H.
Published: July 2002

The intermittency profile in the turbulent flat-plate zero pressure-gradient boundary-layer and a thick axisymmetric boundary-layer has been computed using the Reynolds-averaged k−ε−γ model, where k denotes turbulent kinetic energy, ε its rate of dissipation, and γ intermittency. The Reynolds-averaged model is simpler compared to the conditional model used in the literature. The dissipation equation of the Reynolds-averaged model is modified to account for the effect of entrainment. It has been shown that the model correctly predicts the observed intermittency of the flows. [S0098-2202(00)02403-2]
The Effects of Patch Properties on the Debonding Behavior of Patched Beam-Plates
Authors: Karlsson A. M.
Published: July 2002

The debonding characteristics of patched structures are investigated in this study by means of an analytical model. In particular, the effects the lay-up sequence and edge-tapering of a carbon-reinforced epoxy patch, as well as the beveling of an aluminum patch, have on the initiation, stability, and extent of the debonding are considered. The results presented show that both the degree of edge-tapering and the patch properties must be carefully selected in order to optimize the patched structure. It is also shown that when designing a patched system, it is important to model the correct boundary and load conditions to correctly simulate the debonding behavior. [S0094-4289(00)02204-0]
Error Analysis of Head-Disk Spacing Measurements Made by Using Optical Interferometry
Authors: Mitsuya Yasunaga , Ohshima Yasuji
Published: July 2002

An analytical and simplified method was developed for predicting error propagation encountered when optically measuring head-to-medium spacing in magnetic disk drives. Two kinds of optical interferences observed between the flying head and the glass disk were considered. The first is the homodyne interferometry in which the spacing is obtained from light intensity variation due to interference. The second is polarization interferometry in which the spacing is determined from the phase difference between the parallel and perpendicular components of polarized light. To analytically predict the amount of error propagation, the interference intensity must be presented as a function of its maximum and minimum values which determine the calibration curve. For this purpose, two kinds of accurate and useful approximations were introduced; one is for homodyne interferometry and the other is for polarization interferometry. Using these approximations, the calibration curves were presented in terms of the detected signal and its extremum. Calculation examples were demonstrated for typical head-medium interface conditions and the contribution of error components to the error in spacing measurement was clarified.
High Spatial Resolutive Method Observing the Lubricant Distribution on Magnetic Recording Media
Authors: Kumagai Akiyasu , Orikasa Hitoshi , Takahashi Nobuyuki , Ishiwata Osamu
Published: July 2002

A new method to evaluate the distribution of perfluoropolyether lubricant on hard disks was developed. We used a scanning probe microscope (SPM) technique with the dynamic force mode to detect the adhesion between the tip and the lubricant layer. We found that the distribution of phase of the cantilever oscillation varied with the cantilever amplitude when hard disks were observed, and that the behavior of how the phase image varies with the cantilever amplitude gives the distribution of the lubricant. The relative lubricant amount estimated by this method was linearly correlated with the lubricant thickness measured by Fourier transform infrared spectroscopy (FT-IR). This suggested that the method could quantitatively evaluate the lubricant distribution. Visualization of the lubricant distribution showed that the lubricant was thicker at the bottoms and thinner at the bevels around grooves in the mechanical texture. [S0742-4787(00)02104-4]
Reactive Flow in a Porous Medium: Formulation for Spatially Periodic Hexagonally Packed Cylinders
Authors: Rajesh G. , Bhagat R. B. , Fichthorn K. A.
Published: July 2002

This study develops an integrated micro-macro model of reactive flow in a porous medium consisting of spatially periodic hexagonal array of solid reacting cylinders. The micro model describes the growth of reaction product on the solid reactant surface. The macro flow of the infiltrant fluid is described by Darcy’s law. The transient permeability and thus advancement of the infiltration front are determined as a function of process parameters from the micro model. Crucial process parameters that influence the advance of the fluid front are identified. The results from this investigation can be used to optimize the manufacture of ceramic-matrix composites. [S0021-8936(00)02703-3]
Energy-Based Stochastic Estimation for Nonlinear Oscillators With Random Excitation
Authors: Roberts J. B. , Vasta M.
Published: July 2002

A physically based averaging procedure is applied to a general form of a nonlinear single-degree-of-freedom equation, with nonwhite random excitation, leading to a one-dimensional continuous Markov model for the energy envelope. It is demonstrated that, in combination with an energy-based technique for estimating the potential energy function, the Markov model can be used as the basis of a stochastic identification method for estimating the spectrum of the excitation, the static nonlinear restoring characteristic, and the nonlinear damping function, from measurements of the response alone. Moreover it is shown that, by combining results for two levels of stochastic excitation, it is possible to obtain good estimates of damping and stiffness parameters, both linear and nonlinear. [S0021-8936(00)02304-7]
Theoretical Model of Metal V-Belt Drives During Rapid Ratio Changing
Authors: Carbone G. , Mangialardi L. , Mantriota G.
Published: July 2002

Today the use of metal V-belt (MVB) on C.V.T. (continuously variable transmission) based systems is the rule in automotive applications. The great advantage of this kind of belt is the capability to resist the moving half-pulley’s high axial thrust necessary to transmit the large torque involved. This paper suggest a theoretical model of belt’s behavior during rapid ratio speed changes with the aim to represent the dynamical response of the system during the transient condition. The paper proposes a relation which correlates some easily measurable macroscopic quantities: axial thrust, torque transmitted and belt’s tensions on the slack and tight side. The metal V-belt consists of wedge-shaped plates that are supported by a flexible band, of which there are two types: the metal V-belt without clearance and the metal V-belt with clearance between plates. Our investigation is carried out for the first type of belt and under the hypothesis that there is a rapid variation of speed ratio. The result, that has been reached, allows to predict the behavior of the system and simplifies the planning of continuously variable transmission with metal V-belt.
Analysis of the Thermal Stress and Strain on Arrigo Fiammingo’s Artistic Window in the Cathedral of Perugia
Authors: Buratti Cinzia
Published: July 2002

Thermal stress can damage fragile materials such as glass. It is a worrisome problem if the glass is a work of art, such as the polychromatic window of Arrigo Fiammingo (1565), in the Cathedral of Perugia, the topic of this paper. The window surface, irradiated by sunlight, suffers different thermal stresses, according to the color of the glass elements. In the present paper a calculation of stresses and strains on the window is carried out, for different temperature distributions due to sunlight, by using the ANSYS 5.3 software program. Results are compared with the actual state of the fissures on the window.
Effects of Pulsation on Grid-Generated Turbulence
Authors: Shahidinejad S. , Jerphanion I. , Magaud F. , Souhar M.
Published: July 2002

The effects of low frequency, large amplitude sinusoidal pulsation on grid-generated turbulence (PGGT) were experimentally studied. Two-component hot wire anemometry technique was used. Pulsation did not change homogeneous, isotropic character of grid-generated turbulence.
New Reworkable High Temperature Low Modulus (in Excess of 400–500 °C) Adhesives for MCM-D Assembly
Authors: Wu Jiali , Pike Randy T. , Sitaraman S. K. , Wong C. P.
Published: July 2002

Large area substrate processing is a key solution for improving the productivity of multi-chip module deposition (MCM-D) technology. This project is focused on high temperature low modulus polymeric adhesives for attachment of silicon tiles to suitable pallets to facilitate large area film processing of MCM structures. Current high temperature polymeric materials are predominately polyimide-amide, siloxane modified polyimide-amide, Bisbenzocyclcobutene (BCB), and polynorbornene materials, all of them are neither reworkable nor flexible, which creates an obstacle to remove the coated substrates and to reuse the high cost pallets. However, one of the approaches to address this demand is introducing a low modulus elastic material combined with a unique thermal stabilizer, which will be thermally stable at 400°C for 1 h and thermally degradable at 450°C after 1 h. A series of novel reworkable high temperature (in excess of 400–450°C) adhesives have been developed in this study, that can meet the requirements of adhesion, viscosity, low modulus, thermal stability, and reworkability for MCM-D mass production. The mechanism of thermal stabilizer functionality and adhesive reworkability is presented in this study. In addition, finite element modeling is used to predict the out-of-plane warpage, axial, and interfacial stresses of the tiles-on-pallet palletized assemblies. [S1043-7398(00)00501-6]
Natural Pumice by XPS
Authors: Rossi Antonella , Venezia Anna Maria , Floriano M. A. , Deganello Giulio
Published: July 2002

X-ray photoelectron spectroscopy was used for characterizing pumice: it is a natural aluminosilicate with a high percentage of silica (~70%), a low surface area (~5 m2 g−1 as determined by the BET method) and a density of 2.3 g cm−3. It has a fine, porous physical structure which makes the material easy to machine and also determines its abrasive property. In contrast to the zeolites, pumice has an amorphous structure. Apart from its main use in the construction industry, pumice has begun to be of scientific interest when used as a support for metallic catalysts. Core and valence spectra were compared with standard Al2O3 and SiO2. The aim of this study is to examine the surface of this material.
Titanium Casting with Sand Foundry Techniques
Authors: Lee Warren
Published: July 2002

The ability to produce a east titanium configuration has a history of approximately 10 years. It is presently being done in the United States by six companies. Casting of titanium is no simple task when one considers the thousands of foundries in existence producing cast parts from other metals. The difficulties are that titanium must be handled more carefully because molten titanium is very reactive to liquids, gases, and solids. At present, consumable vacuum arc melting offers the only suitable commercial method of producing titanium castings. The rapid contamination of titanium at elevated temperature by oxygen and nitrogen and the severe damage to ductility by small percentages of such contaminants requires that melting of titanium be done in the absence of air. Because liquid titanium is an extremely effective solvent, problems of containing the molten metal within a crucible during the melting operation are encountered. A water-cooled copper crucible is used to extract heat so rapidly from the liquid metal that it solidifies before its solvent reaction can take effect. This provides a thin film of solid titanium between the molten titanium and the copper crucible. This is referred to as skull melting. The liquidus to solidus range of titanium is quite narrow and problems of fluidity exist. When enough molten titanium is accumulated in the crucible, the power is cut, the electrode is rapidly withdrawn, and the pot is tilted, all within a few seconds or the pool will solidify. A centrifuge is used within the furnace vacuum chamber during the pouring of the melt. The high g forces during the casting operation help overcome the lack of fluidity. The centrifuge action assists in filling mold cavities with metal densities vastly superior to those from conventional sand foundry static casting. Conventional materials such as sand, shell, or ceramic molds are unsatisfactory for titanium since titanium above or near its melting point will violently react with these materials. A water soluble, expendable graphite mold system is a relatively new development in titanium casting and configurations with close tolerances and excellent surface finish are obtainable. New information related to the production of titanium castings with the latest applied technology was presented.
Accurate, Wide Range Ultrahigh-Vacuum Calibration System
Authors: Fowler Peter , Brock F. J.
Published: July 2002

A new method has been investigated for ultrahigh-vacuum calibration (molecular beam calibration) of vacuum gauges and mass spectrometers over the range 10−6−10−15 Torr with less than 5% probable error. The method is applicable, in principle, to all gases but limited in practise to gases with critical temperatures greater than or equal to that of nitrogen. It combines the techniques of pressure attenuation and molecular beaming from a nearly ideal aperture to generate a precisely known molecular density in a volume, the walls of which have a capture coefficient of near unity. The upstream (reference) pressure is measured by an instrument for which NBS has a test schedule. Direct beam to background density ratios in excess of 800:1 were measured for a 304 K argon beam. The conductance of the porous Vycor pressure-attenuating element is constant to pressures exceeding 5000 Torr. Determination of the magnitude of deviations from free molecular flow as the gas mean-free path λ in the furnace approaches the furnace orifice diameter d showed no greater than 12% deviation for λ/d≥25. The measured density distribution in the cryopumped beam tunnel agrees with the expectations of kinetic theory.
Extraction of Structural Information from LEED
Authors: Duke C. B. , Tucker C. W.
Published: July 2002

The inelastic-collision model of LEED using isotropic s-wave scatterers (phase shift π/2 and damping parameter 8 Å) describes the qualitative features of experimental intensity profiles from clean surfaces. For energies above ca. 100 eV, theoretical and experimental profiles give strong scattering near the kinematical positions. From this result, the crystal structure and exposed face can be determined using the kinematical model. For a (2×2) chemisorbed monolayer, calculated intensity profiles of the extra beams show considerable, substrate-dependent, structure. However, the integrals of these profiles over a wide voltage range are in excellent agreement with the predictions of the kinematical model for the absorbate layer alone. This result is independent of the substrate, the phase shifts used to describe the adsorbate, and the position of the adsorbate normal to the substrate. Consequently, extensive structural information can be extracted from LEED using the kinematical model without making a dynamical calculation.
Thermal Expansion at a Surface
Authors: Allen Roland E.
Published: July 2002

A procedure is developed for calculating the thermal expansion near a solid surface. A rough argument indicates that, at high temperatures, αsurface/αbulk≈34〈uz2〉surface/〈uz2〉bulk, where α is the thermal expansion coefficient and 〈u z2〉 is the mean-square amplitude of vibration normal to the surface.
Effect of Steps on Low-Energy Electron Diffraction Intensity Profiles
Authors: Laramore G. E. , Houston J. E. , Park Robert L.
Published: July 2002

A method is described for calculating the electron-solid elastic scattering amplitude when the surface area covered by the coherence width of the electron beam contains a relatively small number of steps. From this it is possible to calculate in detail the angular distribution of the scattered intensity for low-energy electron diffraction. In analogy with the perfect surface case, intensity profiles are defined which characterize the variation with primary beam energy of the central intensities for the various beams. It is shown that a step distribution reduces the central beam intensities with respect to the perfect surface case and also acts to shift the Bragg peaks in the intensity profiles to higher energies. Model calculations for simple step distributions are compared with Jona's experimental data for Al(110). For many adsorbed overlayer systems the problem of domains is simply a special case of our treatment
Controlled rf-sputter etching using atomic absorption spectroscopy
Authors: Bauer H. J. , Bogardus E. H.
Published: July 2002

An apparatus is described based on the principle of atomic absorption spectroscopy to monitor the removal of metallic layers in an argon glow discharge. The apparatus is shown to be particularly advantageous for rf-sputter etching process control of composite metal films, such as in pattern formation for semiconductor device interconnection. Experimental results of the monitoring of the chromium removal while sputter etching CrAgCr “sandwich” films are presented.
Structural and electronic properties of metal-silicide/silicon interfaces: A first-principles study
Authors: Yu Byung Deok , Miyamoto Yoshiyuki , Sugino Osamu , Sakai A. , Sasaki T. , Ohno T.
Published: July 2002

By employing first-principles total-energy calculations we studied the electronic and structural properties of the NiSi2/Si(001) and CoSi2/Si(001) interfaces. We found a new structural model that is energetically more stable than previously proposed models and well explains an experimentally observed 2×1 interfacial ordering. The new model is characterized by sevenfold-coordinated interface metals and interface Si dimers, and is achieved by compromising the bonding configuration of the interface metals and the reduction of the number of interface Si dangling bonds. The underlying mechanism of the model is in contrast to that of a semiconductor-surface reconstruction. Finally, the interfacial electronic properties are also presented to give a physical insight into the microscopic mechanism for the Schottky-barrier formation at metal/semiconductor junctions.
Effect of interface trapping on the frequency response of a photodetector
Authors: Das N. R. , Deen M. Jamal
Published: July 2002

In this article, the effect of carrier trapping at the heterointerface of a p-i-n photodetector (PD) on the frequency response and, hence, on the transit-time limited bandwidth of the PD has been investigated. The effective height of the potential barrier at the valence-band and conduction-band interfaces has been calculated as a function of bias voltage and grading layer thickness taking Al0.2Ga0.8As/GaAs structure as an example. It is shown how the results can be used to estimate the barrier height without doing exact calculations. The barrier heights are used to calculate the rate of emission of carriers from the trap by solving the rate equation. Then, an expression for the photocurrent is derived to study the frequency response of a resonant-cavity-enhanced p-i-n photodetector and hence to obtain its transit-time limited bandwidth. The results from the model are shown to be in good agreement with experimental data.
Chemisorption during catalytic reaction on metal surfaces
Authors: Boudart M.
Published: July 2002

Chemisorption of dihydrogen, dioxygen, and dinitrogen on metal surfaces during reactions of hydrogenation, oxidation, and dinitrogen fixation appears generally to take place after crossing an activation barrier. The nature of this barrier is unknown and the state of the chemisorbed intermediate is, in all cases, a matter of conjecture based on ingenious but indirect observations. In the case of metals, the state of the catalytic surface appears to be very different from that of a clean surface. The definition of a working catalytic surface must include all the surface species of the catalyst in its working state.
Electrochromism in WO3 films with BaO additions
Authors: Molnar B. J. , Haranahalli A. R. , Dove D. B.
Published: July 2002

Films of WO3 with various amounts of BaO additions were deposited from multiple evaporation sources onto glass substrates heated to 100°C. The atomic percent of Ba in each film with respect to W was determined using particle-induced x-ray emission analysis (PIXIE). Compositional variations with film depth were examined using Auger electron spectroscopy combined with ion beam milling. The electrochromic coloration and decoloration behavior was measured in an electrochemical cell. It was found that additions of Ba as small as 10 at. % measurably reduced the amount of coloration induced per given amount of charge injected into the film. The amount of inhibition of electrochromic coloration was found to increase with increasing Ba concentration. At Ba concentrations greater than 45% the coloration effect was virtually eliminated. Ba additions greater than 45 at. % were also found to induce crystallization in the films.
(110) surface states of GaAs and matrix element effects in angle-resolved photoemission
Authors: Chadi D. J.
Published: July 2002

The relaxed (110) surface electronic structure of GaAs is calculated within the tight-binding model. The symmetry and dispersion of the surface states are compared to those measured by angle-resolved photoemission experiments. Variations in photoemission intensity with measurement geometry are related to matrix-element modulation effects and it is shown that angle-resolved measurements can give information on the symmetry of surface states.
Photovoltage studies of aluminum–phthalocyanine interfaces
Authors: Murti D. K. , Brillson L. J. , Slowik J. H.
Published: July 2002

A study of metal–organic semiconductor interfaces has been undertaken. This article is devoted to aluminum–phthalocyanine (H2Pc) interfaces. The interfaces were characterized by surface photovoltage spectroscopy (SPS) and x-ray photoelectron spectroscopy (XPS) under ultrahigh vacuum (UHV) conditions. The spectroscopic characterization was followed by electrical characterization (I–V measurements) both in UHV and in air. The results of this study suggest that the surface contamination on phthalocyanine produced by air-exposure is necessary to produce a large band bending. Clean surfaces of phthalocyanine produced by Ar bombardment do not yield large barriers.
Hydrogen chemisorption on the polar surfaces of GaAs
Authors: Bringans R. D. , Bachrach R. Z.
Published: July 2002

The results which we present here show that hydrogen chemisorption on the polar (100) and (1̄1̄1̄) surfaces of GaAs produces dramatic changes in the surface core levels and in the surface bands seen with angle-resolved photoemission. After saturation coverage of hydrogen, achieved with an exposure of 106L while using a cracking filament, the Ga 3d and As 3d core levels showed variation in intensity, binding energy, and shape consistent with bonding of the hydrogen to the surface As atoms. Both As-rich and Ga-rich surfaces were produced in situ by molecular beam epitaxy, and saturation of these surfaces with hydrogen produced the same resultant surface composition and structure. For GaAs(100), the hydrogen saturated surface was seen with LEED and core level spectroscopy to be As rich. Angle-resolved photoemission measurements have enabled us to obtain the dispersion in the surface Brillouin zone of the hydrogen-induced band.
Measurements of the secondary ion mass spectrometry isotope effect
Authors: Schwarz S. A.
Published: July 2002

The heavier isotopes of a given element are generally underrepresented in the secondary ion mass spectrometry mass spectrum since they emerge from the sample with lower average velocity and are therefore less likely to be emitted as ions. The relative deviation of an isotope ratio measurement from its expected value is represented in the literature by the parameter α. In this work we report measurements of α as a function of secondary ion energy in high-purity Ge, Mo, Pd, Cd, Sn, and W samples; each of which offers several abundant isotopes for examination. A Cameca IMS-3f magnetic sector instrument is operated in the high-energy resolution mode for these measurements. The α values are determined from weighted least-squares fits to the isotope ratio deviations. Appropriate precautions against beam instability, mass interference, and detector saturation effects are employed. Positive and negative ion emission, induced by O+2 and Cs+ bombardment, respectively, are examined. For monatomic positive ion (M+) emission, the magnitude of α correlates roughly with the secondary ion yields and generally increases with increasing emission energy. In contrast, α values for oxide species (MO+) display an inverse dependence on energy indicating surface emission. For negative ion (M−) emission, α changes sign at low energies indicating that, at low energy, ion emission is dominated by the survival probability of the negative ion while, at higher energies, emission depends on the probability of ion formation by electron attachment. Measured α values for diatomic (M+2, M−2) emission are examined with respect to current models of molecular ion formation.
Determination of the valence electronic structure of condensed trimethylaluminum by photoelectron spectroscopy and molecular-orbital calculations
Authors: Motooka T. , Rockett A. , Fons P. , Greene J. E. , Salaneck W. R. , Bergman R. , Sundgren J.-E.
Published: July 2002

The electronic structure of dimerized trimethylaluminum (TMA), Al2(CH3)6, condensed at low temperatures on clean substrates in ultrahigh vacuum, has been investigated using ultraviolet and x-ray photoelectron spectroscopies together with molecular-orbital (MO) calculations carried out using the self-consistent-field Xα-scattered-wave method. Valence-band spectra revealed three broad peaks centered at ∼15.0, 7.5, and 4.5 eV below the Fermi level. The peaks were assigned, based upon computed MO results, to correspond primarily to C(2s)+H(1s), C(2p)+H(1s), and Al(3p)+C(2p) bonding orbitals, respectively, in dimerized TMA. The wave functions of the upper MO levels corresponding to the 4.5-eV peak were predominantly composed of Al(3p) orbitals.
In-plane geometry of the Si(111)-(√3×√3)Ag surface
Authors: Chang C. S. , Porter T. L. , Tsong I. S. T.
Published: July 2002

The technique of impact-collision ion scattering spectrometry was used to determine the in-plane geometry of the Si(111)-(√3×√3)Ag surface. Comparison of experimental data with computer simulation leads to a substitutional trimer model in which Si honeycombs sit on top of Ag trimers occupying substitutional sites. The separation of the Si and Ag layers is 0.7±0.3 Å and the Si–Ag bond length is 2.66±0.3 Å. We also observed type-A and type-B arrangements of the Si and Ag atoms on the surface, with type B being type A rotated 180° about the surface normal. Our results are consistent with reported scanning tunneling microscopy images and also with a missing top layer model proposed from photoemission and x-ray photoelectron diffraction studies.
A scanning tunneling microscopy study of the surface morphology of supported gold particles
Authors: Thomas P. A. , Lee W. H. , Masel R. I.
Published: July 2002

Scanning tunneling microscopy (STM) was used to examine the surface structure of supported gold particles. STM images of annealed gold particles showed that particles larger than 150 Å have a polyhedral shape and a relatively smooth surface morphology. However, the surfaces of the particles smaller than 60 Å remained highly corrugated even after long annealing times. We believe that the difference in morphology of large and small particles may have some important implications for supported metal catalysis.
Synchrotron-radiation-stimulated tungsten deposition on silicon from W(CO)6
Authors: Zanoni R. , Piancastelli M. N. , Marsi M. , Margaritondo G.
Published: July 2002

We report a synchrotron-radiation-excited photoemission study of the adsorption of W(CO)6 on Si(111)2×1. W(CO)6 is shown to adsorb molecularly on Si at 100 K, and to undergo dissociation at room temperature (RT). Exposure of a reacted surface at 100 K to unmonochromatized synchrotron light results in the formation of a metal layer on Si. Such a metal layer is stable during RT annealing.
Intramolecular imaging of physisorbed molecules with the scanning tunneling microscope at liquid/graphite interface
Authors: Yeo Y. H. , Yackoboski K. , McGonigal G. C. , Thomson D. J.
Published: July 2002

We report on scanning tunneling microscope (STM) images of physisorbed n-decanol at the liquid/graphite interface. The STM image contrast within the molecules is observed to change as a function of bias voltage. The origin of this image contrast is found to be related to the electronic structures associated with the functional groups within the molecules. This enables us to selectively image the molecule’s hydroxyl head group and the alkane tail at different bias voltages.
Chemical vapor deposition of aluminum and gallium nitride thin films from metalorganic precursors
Authors: Hoffman David M. , Prakash Rangarajan Sri , Athavale Satish D. , Economou Demetre J. , Liu Jia-Rui , Zheng Zongshuang , Chu Wei-Kan
Published: July 2002

Nearly stoichiometric aluminum and gallium nitride thin films were prepared from hexakis(dimethylamido)dimetal complexes, M2[N(CH3)2]6 (M=Al,Ga), and ammonia at substrate temperatures as low as 200 °C by using low pressure thermal and plasma enhanced chemical vapor deposition (CVD). Both processes gave films that showed little or no carbon (<5 at. %) and no oxygen (<few at. %) contamination, but in all cases there was hydrogen incorporation. The films were highly transparent in the ultraviolet and visible regions. The barrier properties of the aluminum nitride films in a Si/AlN/Au metallization scheme were examined by using backscattering spectrometry. The growth rate of the aluminum nitride films was as high as 1300 Å /min. Overall, the results suggest that M2[N(CH3)2]6 (M=Al,Ga) are promising precursors for low-temperature/low-pressure thermal and plasma-enhanced CVD of group III nitride thin films.
Plasma diagnostics and processings in CF4/He radio frequency discharge
Authors: Mutsukura N. , Shimada M.
Published: July 2002

Plasma diagnostics and Si etching were carried out in 13.56 MHz rf CF4 plasma mixed with He. In the plasma diagnostics, density of ion flux reaching electrode, and both ion sheath thickness and dc self-bias voltage at powered electrode were measured. A small amount of He admixture in the CF4 plasma scarcely affects the plasma characteristics, but those greatly change when a few percent of CF4 is added into a He plasma: the ion sheath thickness greatly decreases and the self-bias voltage increases. This remarkable change was considered to be due to the CF4/He discharge becoming electronegative. The He admixture can produce additional CFn+ ions by deexcitation processes with both excited He* atoms and He+ ions, which affect considerably the Si etching rate and etching anisotropy in plasma etching process.
Langmuir probe measurements in a low pressure inductively coupled plasma used for diamond deposition
Authors: Okada Katsuyuki , Komatsu Shojiro , Matsumoto Seiichiro
Published: July 2002

The characterization of 13.56 MHz low pressure inductively coupled plasmas used for diamond deposition has been performed with a Langmuir probe. The plasma potential (Vp), electron temperature (Te), electron density (Ne), ion density (Ni), and electron energy distribution function (EEDF) were measured in a CH4/H2 plasma with 10–50 mTorr of the gas pressure at 1 kW of the plasma power, and were compared with those of an Ar plasma. We found that the Vp, Ne, and Ni have a similar radial distribution, which has a peak at the center axis and decreases outward in the radial direction, while the Te is almost constant within the radius of 20 mm and slightly decreases toward the chamber wall. It was also found that with increasing pressure the Vp and the Te decrease, whereas the Ne increases, except for a CH4/H2 plasma at 50 mTorr. The transition from a Maxwellian distribution to a Druyveysten distribution was observed at 10 mTorr in the EEDFs of Ar plasmas, while it occurred at 20 mTorr in CH4/H2 plasmas. The EEDF of a CH4/H2 plasma at 50 mTorr has a hump at ∼6 eV corresponding to the resonant peak of the vibrational excitation cross section of CH4 molecule.
Improvement of the inverted GaAs/AlGaAs heterointerface
Authors: Fischer R. , Masselink W. T. , Sun Y. L. , Drummond T. J. , Chang Y. C. , Klein M. V. , Morkoç H. , Anderson E.
Published: July 2002

The luminescent properties of thin single quantum well AlxGa1−xAs/GaAs structures grown by molecular beam epitaxy were investigated. Since the photoluminescence response of these structures is dominated by the quality of the heterointerfaces, and particularly the inverted heterointerface, the effect of using several different types of interfaces was investigated. In structures with conventional abrupt heterointerfaces, only weak luminescence dominated by extrinsic processes was observed. By grading the Al mole fraction over ∼150 Å region at the heterointerface, an eightfold improvement in the excitonic photoluminescent intensity was obtained. By inserting a three-period superlattice of graded average composition, a 160-fold improvement in the excitonic photoluminescent intensity over the abrupt interface structure was obtained. The effect of using dimeric arsenic was also investigated. Since these structures provide feedback as to the quality of the heterointerfaces they can be used as a means of finding ways to improve them.
Simulations of metalorganic chemical vapor deposition and of cluster formation on GaAs
Authors: Menon Madhu , Allen Roland E.
Published: July 2002

A new technique for realistic simulations of molecular motion has been improved in several respects. Most dramatically, the computational expense has been reduced by another order of magnitude, through a mathematical procedure that reduces the original pair of complex nonHermitian matrices to a single real symmetric matrix. Simulations have been performed for Ga(CH3)3, Al(CH3)3, and As(CH3)3 molecules and for four-atom Al and Sb clusters on GaAs(110). A variety of initial configurations after chemisorption are observed for each of these systems. The energetically most stable configuration observed for Ga(CH3)3 is one in which this molecule has a highly symmetric planar geometry, with the plane of the molecule perpendicular to the surface. Dissociation is not observed in these simulations, which are at low temperature and which last for only 1 ps. In most cases the trimethyl molecules tend to perturb the semiconductor surface only weakly. Al shows a much stronger tendency to cluster than Au. Also, the Al atoms within the cluster tend to lie at sites of high symmetry, as defined by the substrate. For Sb clusters, states are observed in the upper part of the band gap.
Photolithographic patterning of porous silicon
Authors: Couillard J. G. , Craighead H. G.
Published: July 2002

Regions of light-emitting porous silicon fabricated by anodic electrochemical etching have been patterned by photolithography. Samples were spin-coated with photoresist, and contact photolithography was used to define the desired mask pattern. Exposure of unmasked sample regions to an isotropic oxygen plasma in a barrel reactor results in a dramatic reduction of the visible photoluminescence. The resulting patterns exhibit high contrast, with a minimum feature size of 4 μm. The patterns are remarkably stable, withstanding both chemical treatment and atmospheric contamination.
Concepts in competitive microelectronics manufacturing
Authors: Liehr Michael , Rubloff Gary W.
Published: July 2002

While progress in the microelectronics industry is gated by the frontiers of high technology and its underlying science, competitiveness in this industry is determined at least as much by how effectively the relevant science and engineering are integrated to address those issues central to manufacturing. Competitive manufacturing places a premium on such factors as rapid learning in technology development and yield enhancement, process and factory control, minimization of capital costs, and equipment and product reliability, all factors which synthesize the individual science and engineering elements associated with microelectronics technology. This paper is a primer for research aimed at impacting microelectronics manufacturing science and technology. After presenting an overview of competitiveness requirements for manufacturing, it focuses on strategic elements: advanced process equipment, process/materials characterization and real time process control, defect identification/control and reliability, three-dimensional processing and manufacturability, and process integration.
Comparison of Immunogenicity and Safety of a Virosome Influenza Vaccine with Those of a Subunit Influenza Vaccine in Pediatric Patients with Cystic Fibrosis
Authors: Schaad U. B. , Bühlmann U. , Burger R. , Ruedeberg A. , Wilder-Smith A. , Rutishauser M. , Sennhauser F. , Herzog C. , Zellmeyer M. , Glück R.
Published: July 2002

The objective of this study was to compare the immunogenicity and safety of a single-dose regimen and a two-dose regimen of a trivalent virosome influenza vaccine (Inflexal Berna V) with those of a trivalent subunit influenza vaccine (Influvac) in children and adolescents with cystic fibrosis (CF). In an open, randomized, multicenter study with parallel groups, 11 young children with CF (1 to 6 years old) and 53 older children and adolescents with CF (>6 years old) were randomly assigned to one of the following immunization regimens: virosome vaccine at 0.5 ml on study day 0 or 0.25 ml on days 0 and 28 or a standard regimen of subunit vaccine, i.e., 0.5 ml on day 0 for older children and 0.25 ml on days 0 and 28 for younger children. Safety assessments, i.e., recording of systemic and local adverse events (AEs) and vital signs, were made for a 5-day observation period after each immunization. Hemagglutination inhibition (HI) titers were determined at baseline and 4 weeks after the single-dose and the two-dose immunizations, respectively. Immunogenicity was assessed according to the criteria of the European Agency for the Evaluation of Medicinal Products (EMEA). Both vaccines induced comparable HI antibody titers. Seroconversion (≥4-fold rise in HI antibody titers, reaching a titer of ≥1:40) was achieved in 41 to 100% of the participants. Seroprotection (HI titer, ≥1:40) and a >2.5-fold increase in geometric mean titers were achieved in 100% of the participants. Thus, all three EMEA requirements for influenza vaccine efficacy were met by all treatment groups and for both vaccines. The virosome vaccine, when administered as a single dose, seemed to induce superior immunogenicity compared with the standard pediatric two-dose regimen. Totals of 42 and 57% of vaccinees receiving virosome and subunit vaccines, respectively, reported at least one local AE (predominantly pain). Totals of 84 and 71% of subjects receiving virosome and subunit vaccines, respectively, complained in response to questions of at least one systemic AE (mainly cough, fatigue, coryza, or headache). The majority of events were mild or moderate and lasted 1 or 2 days only. No obvious relationship was found between AE reporting rate and vaccine formulation, age group, or dose regimen. The relatively high AE reporting rate seemed to be partly related to the symptomatology of the underlying CF disease. In summary, the virosome and subunit vaccines induced in both age groups and against all three influenza strains an efficient immune response and were well tolerated by the children and adolescents with CF.
Cyclic AMP and Fluconazole Resistance in
Saccharomyces cerevisiae
Authors: Kontoyiannis D. P. , Rupp Steffen
Published: July 2002

Cyclic AMP (cAMP) is involved in the stress response in
Saccharomyces cerevisiae
. We show that cAMP is required for resistance to fluconazole in
S. cerevisiae
. In addition, activation of
Ras2
, a regulator of cAMP generation, results in some protection from fluconazole toxicity in a fashion independent of the efflux transporter Pdr5p.
Serologic Testing for Celiac Disease in the United States: Results of a Multilaboratory Comparison Study
Authors: Murray Joseph A. , Herlein Judith , Mitros Frank , Goeken James A.
Published: July 2002

The aim of this study was to compare the efficiencies of six reference laboratories for serologic testing for celiac disease. Serum from 20 patients with untreated celiac disease and from 20 controls was thawed, divided, and distributed to each participating laboratory, which performed endomysial antibody tests. Five laboratories also performed antigliadin antibody tests. Sensitivity for endomysial antibody immunoglobulin A (IgA) varied from 57 to 90%. In all laboratories, the specificity for celiac disease was 100%. The sensitivity and specificity for both IgA and IgG antigliadin antibody varied significantly. When results from all three tests were combined in each laboratory, sensitivity was 90 to 100%. The specificity for endomysial antibody was 100% in the laboratories. Sensitivity was less than reported previously. Standardization of these tests is needed in the United States.
Binding of a Monoclonal Antibody to Sporozoites ofSarcocystis singaporensisEnhances Escape from the Parasitophorous Vacuole, Which Is Necessary for Intracellular Development
Authors: Jäkel T. , Wallstein E. , Müncheberg F. , Archer-Baumann C. , Weingarten B. , Kliemt D. , Mackenstedt U.
Published: July 2002

Early intracellular development in vitro of the cyst-forming protozoonSarcocystis singaporensisand the influence of a monoclonal antibody on invasion, intracellular localization, and development of sporozoites were studied. As revealed by immunofluorescence using parasite-specific antibodies which labeled the parasitophorous vacuole membrane (PVM) and by ultrastructural analysis, sporozoites invaded pneumonocytes of the rat via formation of a parasitophorous vacuole (PV). About half of the sporozoites left this compartment within the first 8 h postinfection to enter the host cell cytosol. By semiquantitative analysis of acetyl-histone H4 expression of sporozoites, a marker linked to early gene expression of eukaryotic cells, we show (supported by ultrastructural analysis) that escape from the PV appears to be necessary for early intracellular development. More than 90% of sporozoites located in the cytosol expressed high levels of acetylated histone H4 in the nucleus, whereas only a quarter of the intravacuolar sporozoites exhibited a similar signal. As revealed by ultrastructural analysis, young schizonts all resided in the cytosol. Specific binding of a monoclonal antibody (11D5/H3) to sporozoites before invasion significantly enhanced their escape from the PV, whereas cell invasion itself remained unaffected. The antibody actually increased proliferation of the parasites in vitro, providing a further link between residence in the cytosol and successful intracellular development. Monoclonal antibody 11D5/H3 precipitated a major 58-kDa antigen from oocyst-sporocyst extracts and reacted with the cytoplasm and the surface of sporozoites in immunofluorescence assays. Collectively, the observed antibody-parasite interaction suggests the existence of a signaling event that influences intracellular development ofSarcocystis.