bluuebunny/crossref_metadata_2025 huggingface dataset:
Strategic Information Systems Planning: Its Adoption and Use
Authors: Rogerson Simon , Fidler Christine
Published: July 2002

Advances in information provision have led organizations to attempt to
develop IS/IT strategies which interrelate with their business
strategies and which together support corporate missions. Strategic
information systems planning (SISP) has become an accepted part of the
overall corporate strategic planning process. The proliferation of
methods and the variations in satisfaction indicate a need to provide a
framework for classifying and comparing SISP approaches which will
provide guidance on use and to explain why certain approaches are more
commonly used than others. Develops a classification framework based on
complexity and describes tools for using the framework. Provides
indication as to the nature of a complete classification and comparison
method for SISP based on complexity, scope and fit.
Museums and galleries on the Internet
Authors: Taylor Janet H. , Ryan Joe
Published: July 2002

A new form of “museum” has emerged which takes advantage of the
Internet′s seemingly limitless format options for electronic
presentation and ability to tailor in‐depth presentations to niche
audiences. Constraints of ownership and geographic location are lessened
as Internet‐based museums point to sources across the globe. Collections
which are physically impossible to construct are being mounted
electronically. Offers a sampler of museums and galleries around the
world which are making use of WorldWide Web or Gopher servers.
Webmasters as mass media gatekeepers: a qualitative exploratory study
Authors: Beard Fred , Olsen Rolf L.
Published: July 2002

Eight college and university Webmasters in three midwestern states were interviewed to explore their communications practices and activities by applying a traditional mass media gatekeeping perspective. The results suggest that gatekeeping theory is a valuable approach for studying individuals responsible for the mediation of messages in the emerging online media. Webmasters’ personal characteristics and attitudes were found to influence their media content decisions, they share common values used to determine content and design, and they face a variety of organizational and related constraints, some exclusive to Web gatekeepers in an academic setting. Examples of gatekeeping activity and observations by the informants are presented, and suggestions for future research are included.
A cointegration approach to the price dynamics of private housing. A Singapore case study
Authors: Ho Kim Hin David , Calero Cuervo Javier
Published: July 2002

This paper looks into the dynamics of private housing prices in Singapore from the first quarter of 1985 to the fourth quarter of 1995. Employing the cointegration analysis, the paper shows that overall private housing price is cointegrated with real gross domestic product, prime lending rate and private housing starts. An error‐correction mechanism is also incorporated in the estimation of changes in the overall private housing price to account for the short‐run deviations from the equilibrium relationship among these variables.
Structural features of a zinc binding site in the superantigen strepococcal pyrogenic exotoxin A (SpeA1): Implications for MHC class II recognition
Authors: Baker Matthew , Gutman Delia M. , Papageorgiou Anastassios C. , Collins Carleen M. , Acharya K. Ravi
Published: July 2002

Streptococcal pyrogenic exotoxin A (SpeA) is produced by Streptococcus pyogenes, and has been associated with severe infections such as scarlet fever and Streptococcal Toxic Shock Syndrome (STSS). In this study, the crystal structure of SpeA1 (the product of speA allele 1) in the presence of 2.5 mM zinc was determined at 2.8 Å resolution. The protein crystallizes in the orthorhombic space group P21212, with four molecules in the crystallographic asymmetric unit. The final structure has a crystallographic R‐factor of 21.4% for 7,031 protein atoms, 143 water molecules, and 4 zinc atoms (one zinc atom per molecule). Four protein ligands—Glu 33, Asp 77, His 106, and His 110—form a zinc binding site that is similar to the one observed in a related superantigen, staphylococcoal enterotoxin C2. Mutant toxin forms substituting Ala for each of the zinc binding residues were generated. The affinity of these mutants for zinc ion confirms the composition of this metal binding site. The implications of zinc binding to SpeA1 for MHC class II recognition are explored using a molecular modeling approach. The results indicate that, despite their common overall architecture, superantigens appear to have multiple ways of complex formation with MHC class II molecules.
Reduced NR2A expression and prolonged decay of NMDA receptor‐mediated synaptic current in rat vagal motoneurons following axotomy
Authors: Nabekura Junichi , Ueno Tsuyoshi , Katsurabayashi Shutaro , Furuta Akiko , Akaike Norio , Okada Masayoshi
Published: July 2002

To elucidate characteristic changes in the N‐methyl‐d‐aspartate (NMDA) receptor on neurons following axotomy, subunit expressions and functional features of the NMDA receptor were examined in the dorsal motor nucleus of vagus (DMV) of rats receiving vagal axotomy at the neck. Western blotting analysis demonstrated that the expression of NR2A decreased 2–3 days after in vivo axotomy, while expression of NR1 and NR2B, NR2C and NR2D subunits did not change significantly. To examine the functional changes, patch clamp recordings in whole‐cell mode were employed on the axotomized DMV neurons identified by retrograde labelling with fluorescent dye. The amplitude ratios of ifenprodil‐sensitive components of NMDA response and d,l‐2‐amino‐5‐phosphovaleric acid (APV)‐sensitive evoked postsynaptic current increased after axotomy. In addition, APV‐sensitive postsynaptic currents exhibited a longer decay time in identified axotomized vagal motoneurons than in control neurons. No significant differences in the current density of the NMDA response and the peak amplitude of APV‐sensitive synaptic currents were observed between axotomized and intact DMV neurons. In conclusion, a decrease in NR2A expression results in the appearance of functional characteristics of the NMDA receptor predominantly containing the NR2B subunit. This might lead to a long‐term increase of the susceptibility of neurons to excitotoxicity.
Vibration-Based Damage Identification in Structures Exhibiting Axial and Torsional Response
Authors: Duffey T. A. , Doebling S. W. , Farrar C. R. , Baker W. E. , Rhee W. H.
Published: July 2002

A method is derived to detect and localize linear damage in a structure using the measured modal vibration parameters. This method is applicable when the vibration strain energy is stored in the axial or torsional modes, which differentiates it from previously derived strain-energy-based methods. The new method is compared to the previously derived flexibility-change method for comparison. Both methods are verified by application to an analytical eight degree of freedom model. Experimental validation for both methods is also presented by application to an experimental eight degree of freedom spring-mass structure.
Mechanics and Physics of Brittle to Ductile Transitions in Fracture1
Authors: Argon A. S.
Published: July 2002

The mechanisms of brittle-to-ductile transition of fracture in intrinsically brittle crystalline solids such as structural steel have been of great technological interest for a long time. While much useful phenomenology on this important bifurcation behavior has evolved through material testing and alloy development throughout the period following the large scale fractures in Liberty ships during and after World War II, fundamental mechanistic understanding has been lacking until recent times. Over the past decade or so, a renewed level of interest has resulted in a number of fundamental studies of both experimental nature and modeling of crack-tip response which demonstrated a remarkable connection of atomic level processes at tips of cleavage cracks and the macroscopic fracture transitions. These mechanistic connections have not only gone a long way in providing basic rationale for some of the successful empirical practices in alloy design and microstructure control, but clear the way for further advances based on basic atomic level processes governing crystal plasticity. Here we give an overview of some recent developments in this area emanating from our own researches.
Closure to “Discussion: ‘Analysis of the Working Process and Mechanical Losses in a Stirling Engine for a Solar Power Unit’ ” (Prieto, J. I., 2000, ASME J. Solar Energ. Eng., 122, p. 207)
Authors: Makhkamov Kh. Kh. , Ingham D. B.
Published: July 2002

[S0199-6231(00)00804-2]
Modeling of 2-D Leakage Jet Cavitation as a Basic Study of Tip Leakage Vortex Cavitation
Authors: Watanabe Satoshi , Seki Hiraku , Higashi Seiji , Yokota Kazuhiko , Tsujimoto Yoshinobu
Published: July 2002

As the first step of the study of cavitation in the tip leakage flow in turbomachinery, experimental and numerical investigations on characteristics of 2-D leakage jet cavitation are conducted. The experiments using 2-D model apparatus are carried out for three values of initial pressure and for three values of tip clearance. The numerical methods are constructed by combining the vortex method with three types of cavity models. Through the comparisons with the experiments, it is found that one of the models, which takes account of the effects of cavity behavior on the ambient flow, simulate the location and the size of the cavity fairly well in spite of its simplicity.
Vibrations of Tapered Timoshenko Beams in Terms of Static Timoshenko Beam Functions
Authors: Zhou D. , Cheung Y. K.
Published: July 2002

In this paper, the free vibrations of a wide range of tapered Timoshenko beams are investigated. The cross section of the beam varies continuously and the variation is described by a power function of the coordinate along the neutral axis of the beam. The static Timoshenko beam functions, which are the complete solutions of a tapered Timoshenko beam under a Taylor series of static load, are developed, respectively, as the basis functions of the flexural displacement and the angle of rotation due to bending. The Rayleigh-Ritz method is applied to derive the eigenfrequency equation of the tapered Timoshenko beam. Unlike conventional basis functions which are independent of the cross-sectional variation of the beam, these static Timoshenko beam functions vary in accordance with the cross-sectional variation of the beam so that higher accuracy and more rapid convergence have been obtained. Some numerical results are presented for both truncated and sharp-ended Timoshenko beams. On the basis of convergence study and comparison with available results in the literature it is shown that the first few eigenfrequencies can be given with quite good accuracy by using a small number of terms of the static Timoshenko beam functions. Finally, some valuable results are presented systematically.
Improvement of Vibration Damping Capacity and Fracture Toughness in Composite Laminates by the Use of Polymeric Interleaves
Authors: Gibson Ronald F. , Chen Yu , Zhao Hui
Published: July 2002

It is shown that, under certain conditions, simultaneous improvement of vibration damping capacity and interlaminar fracture toughness in composite laminates can be achieved by using polymeric interleaves between the composite laminae. The specific case of Mode II interlaminar fracture toughness and flexural damping capacity of interleaved composite laminates is studied. Graphite/epoxy, E-glass/epoxy and E-glass/polyetherimide composite laminates with polymeric interleaves of several different thicknesses and materials were tested using both the end notch flexure (ENF) test for Mode II fracture toughness and the impulse-frequency response test for flexural damping capacity. The Mode II energy release rate GIIc for all three composites increased linearly with increasing interleaf thickness up to a critical thickness, then dropped off with further increases in thickness. The damping loss factor η for all three composites increased linearly with increasing interleaf thickness up to the maximum thickness. Analytical models for predicting the influence of interleaves on GIIc and η are developed, along with a hypothesis for the critical thickness effect with regard to fracture toughness.
Response of a Model Gas Turbine Combustor to Variation in Gaseous Fuel Composition
Authors: Flores R. M. , Miyasato M. M. , McDonell V. G. , Samuelsen G. S.
Published: July 2002

The effect of fuel composition on performance is evaluated on a model gas turbine combustor designed to mimic key features of practical devices. A flexible fuel injection system is utilized to control the placement of the fuel in the device to allow exploration and evaluation of fuel distribution effects in addition to chemistry effects. Gas blends reflecting the extremes in compositions found in the U.S. are considered. The results illustrate that, for the conditions and configuration studied, both fuel chemistry and fuel air mixing play a role in the performance of the device. While chemistry appears to be the predominant factor in stability, a role is noted in emissions performance as well. It is also found that changes in fuel distribution associated with changes in fuel momentum for fixed firing rate also have an impact on emissions. For the system considered, a strategy for sustaining optimal performance while fuel composition changes is illustrated.
On the Steady Motions of a Rotating Elastic Rod
Authors: Kinkaid N. M. , O’Reilly O. M. , Turcotte J. S.
Published: July 2002

In this paper, a model for the deformation of a rotating prismatic rod-like body is developed and analyzed. The novel feature of the model is its incorporation of the Poisson effect. As a result, it provides realistic solutions for the deformed states of steadily rotating rods. The model presented in this paper is also simplified to a nonlinear version of a classical model for rotating rods. Numerical continuation is used to solve the boundary value problems associated with these models.
DNS of Turbulent Heat Transfer in Channel Flow With Heat Conduction in the Solid Wall
Authors: Tiselj Iztok , Bergant Robert , Mavko Borut , Bajsic´ Ivan , Hetsroni Gad
Published: July 2002

The Direct Numerical Simulation (DNS) of the fully developed velocity and temperature fields in the two-dimensional turbulent channel flow coupled with the unsteady conduction in the heated walls was carried out. Simulations were performed at constant friction Reynolds number 150 and Prandtl numbers between 0.71 and 7 considering the fluid temperature as a passive scalar. The obtained statistical quantities like root-mean-square temperature fluctuations and turbulent heat fluxes were verified with existing DNS studies obtained with ideal thermal boundary conditions. Results of the present study were compared to the findings of Polyakov (1974), who made a similar study with linearization of the fluid equations in the viscous sublayer that allowed analytical approach and results of Kasagi et al. (1989), who performed similar calculation with deterministic near-wall turbulence model and numerical approach. The present DNS results pointed to the main weakness of the previous studies, which underestimated the values of the wall temperature fluctuations for the limiting cases of the ideal-isoflux boundary conditions. With the results of the present DNS it can be decided, which behavior has to be expected in a real fluid-solid system and which one of the limiting boundary conditions is valid for calculation, or whether more expensive conjugate heat transfer calculation is required.
Dynamic Optimization of Human Walking
Authors: Anderson Frank C. , Pandy Marcus G.
Published: July 2002

A three-dimensional, neuromusculoskeletal model of the body was combined with dynamic optimization theory to simulate normal walking on level ground. The body was modeled as a 23 degree-of-freedom mechanical linkage, actuated by 54 muscles. The dynamic optimization problem was to calculate the muscle excitation histories, muscle forces, and limb motions subject to minimum metabolic energy expenditure per unit distance traveled. Muscle metabolic energy was calculated by summing five terms: the basal or resting heat, activation heat, maintenance heat, shortening heat, and the mechanical work done by all the muscles in the model. The gait cycle was assumed to be symmetric; that is, the muscle excitations for the right and left legs and the initial and terminal states in the model were assumed to be equal. Importantly, a tracking problem was not solved. Rather, only a set of terminal constraints was placed on the states of the model to enforce repeatability of the gait cycle. Quantitative comparisons of the model predictions with patterns of body-segmental displacements, ground-reaction forces, and muscle activations obtained from experiment show that the simulation reproduces the salient features of normal gait. The simulation results suggest that minimum metabolic energy per unit distance traveled is a valid measure of walking performance.
A Numerical Analysis of Phonation Using a Two-Dimensional Flexible Channel Model of the Vocal Folds
Authors: Ikeda Tadashige , Matsuzaki Yuji , Aomatsu Tatsuya
Published: July 2002

A two-dimensional flexible channel model of the vocal folds coupled with an unsteady one-dimensional flow model is presented for an analysis of the mechanism of phonation. The vocal fold is approximated by springs and dampers distributed in the main flow direction that are enveloped with an elastic cover. In order to approximate three-dimensional collision of the vocal folds using the two-dimensional model, threshold values for the glottal width are introduced. The numerical results show that the collision plays an important role in speech sound, especially for higher resonant frequency components, because it causes the source sound to include high-frequency components.
Interaction Effects Between Surface Radiation and Turbulent Natural Convection in Square and Rectangular Enclosures
Authors: Velusamy K. , Sundararajan T. , Seetharamu K. N.
Published: July 2002

The interaction effects of surface radiation with turbulent natural convection of a transparent medium in rectangular enclosures have been numerically analyzed, covering a wide range of Rayleigh number from 109 to 1012 and aspect ratio from 1 to 200. The vertical walls of the enclosure are isothermal and maintained at different temperatures. The adiabatic top and bottom walls of the enclosure have been modelled for the limiting cases of negligible or perfect conduction along their lengths. The interaction with surface radiation results in larger velocity magnitudes and turbulence levels in the vertical as well as horizontal boundary layers, leading to an increase in the convective heat transfer by ∼25 percent. Due to the asymmetrical coupling of radiation, the augmentation of convective Nusselt number of the cold wall is larger than that of the hot wall. In tall enclosures, the convective Nusselt number exhibits three distinct regimes with respect to aspect ratio, viz. the slow growth regime, the accelerated growth regime and the invariant (or saturated) regime. The augmentation of convective Nusselt number for perfectly conducting horizontal walls is found to be of similar nature to that in the case with radiation interaction.
A Study on Five Flank Machining of Centrifugal Compressor Impellers
Authors: Tsay D. M. , Chen H. C. , Her M. J.
Published: July 2002

Referring to machining technologies used for turbomachinery components, generally there are two cutting strategies: point cutting and flank cutting. Based on considerations of the cost, efficiency, and surface roughness, flank cutting by using a five-axis machining tool is a promising way to machine blade surfaces of turbomachinery components constructed by ruled surfaces. In this article, a flank cutting technology for centrifugal compressor impellers is developed by using the B-spline curve interpolation, ruled surface construction, and coordinate transformations. Also, an impeller with 12 blades is actually machined to verify the proposed approach by using a five-axis machining center.
Thermal Effects on the Film Thickness in Elliptic EHL Contacts With Entrainment Along the Major Contact Axis
Authors: Kaneta M. , Kawashima R. , Masuda S. , Nishikawa H. , Yang P. , Wang J.
Published: July 2002

The effects of thermal conductivity and kinematics of contacting surfaces and viscosity-pressure coefficient on the film thickness in an elliptical contact under pure sliding conditions in which lubricant entrainment vector is directed along the major principal axis of the contact ellipse are discussed on the basis of experimental and numerical results. In the system where the conjunction is composed of surfaces having a large difference in their thermal conductivities, the film thickness is influenced markedly by the kinematics, in particular when a lubricating oil with a rather high viscosity-pressure coefficient is used. That is, the film thickness is much smaller when the surface having a low thermal conductivity is moving and that having a high thermal conductivity is stationary than in the opposite case. It is also found that a rather large dimple occurred in former case under rather high sliding condition moves toward the exit.
Extracting Articulation Models from CAD Models of Parts With Curved Surfaces
Authors: Sinha Rajarishi , Gupta Satyandra K. , Paredis Christiaan J. J. , Khosla Pradeep K.
Published: July 2002

In an assembly, degrees of freedom are realized by creating mating features that permit relative motion between parts. In complex assemblies, interactions between individual degrees of freedom may result in a behavior different from the intended behavior. In addition, current methods perform assembly reasoning by approximating curved surfaces as piecewise linear surfaces. Therefore, it is important to be able to reason about assemblies using exact representations of curved surfaces; verify global motion behavior of parts in the assembly; and create motion simulations of the assembly by examination of the geometry and material properties. In this paper, we present a linear algebraic constraint method to automatically construct the space of allowed instantaneous motions of an assembly from the geometry of its constituent parts. Our work builds on previous work on linear contact mechanics and curved surface contact mechanics. We enumerate the conditions under which general curved surfaces can be represented using a finite number of constraints that are linear in the instantaneous velocities. We compose such constraints to build a space of allowed instantaneous velocities for the assembly. The space is then described as a set-theoretic sum of contact-preserving and contact-breaking subspaces. Analysis of each subspace provides feedback to the designer, which we demonstrate through the use of an example assembly—a 4-part mechanism. Finally, the results of the analysis of a 4-bar linkage are compared to those from mechanism theory.
The Effect of Debonding Angle on the Reduction of Effective Moduli of Particle and Fiber-Reinforced Composites
Authors: Zhao Y. H. , Weng G. J.
Published: July 2002

In an effort to uncover the effect of interfacial partial debonding on the reduction of composite stiffness, a reduced moduli approach is proposed for the fictitious inclusions which are used to replace the original partially debonded inclusions. The fictitious inclusions are now perfectly bonded to the matrix and any micromechanical theory can be called upon to estimate the moduli of the composite. Using the volume of the inclusion directly beneath the interfacial cracks under the considered loading mode as a measure of damage, a set of anisotropic damage parameters is established in terms of the debonding angle, providing the reduced moduli for the fictitious inclusions. Specific considerations include debonding on the top and bottom of spheres and prolate inclusions, debonding on the lateral surface of spheres and oblate inclusions, and debonding on the top and bottom of circular fibers and elliptic cylinders. The reductions of the five transversely isotropic moduli for the partially debonded particle composites and the nine orthotropic moduli for the partially debonded fiber composites are examined as the debonding angle increases. The theory is also compared with some finite element results, and it suggests that the concept proposed to estimate the reduced moduli of the fictitious inclusions is a viable one.
Acoustic Fatigue of Impellers of Rotating Machinery
Authors: Eisinger Frantisek L.
Published: July 2002

Impellers of air, gas, or steam moving rotating machinery are exposed to acoustic pressure loading (pressure pulsations) from acoustic waves generated in the gaseous medium from flow within the machine casing. The acoustic waves and the impeller structure contain a number of natural frequencies and corresponding mode shapes. The acoustic waves are expressed by pressure pulsations which typically consist of 1) fluctuating wall pressures, 2) plane waves, and 3) higher-order acoustic modes. Out of the three excitation phenomena, the higher-order acoustic modes are the most efficient excitation sources of impeller vibration. The reason for this is the interaction of these modes with impeller structural modes when they become coincident. Of importance is the coincidence of acoustic modes and structural modes with matching wave numbers. The most severe dynamic loading of the impeller occurs at complete coincidence in which in addition to a match in wave numbers (mode shapes) also matching of acoustic and structural frequencies occurs. The paper will provide the theoretical background of the physical phenomena governing the fluid-structure interaction which may lead to extreme loading of the impeller in an acoustically structurally coupled system. Such loading may result in vibration and structural fatigue (acoustic fatigue) and possibly in the destruction of the impeller.
Biomechanical Study of Pediatric Human Cervical Spine: A Finite Element Approach
Authors: Kumaresan Srirangam , Yoganandan Narayan , Pintar Frank A. , Maiman Dennis J. , Kuppa Shashi
Published: July 2002

Although considerable effort has been made to understand the biomechanical behavior of the adult cervical spine, relatively little information is available on the response of the pediatric cervical spine to external forces. Since significant anatomical differences exist between the adult and pediatric cervical spines, distinct biomechanical responses are expected. The present study quantified the biomechanical responses of human pediatric spines by incorporating their unique developmental anatomical features. One-, three-, and six-year-old cervical spines were simulated using the finite element modeling technique, and their responses computed and compared with the adult spine response. The effects of pure overall structural scaling of the adult spine, local component developmental anatomy variations that occur to the actual pediatric spines, and structural scaling combined with local component anatomy variations on the responses of the pediatric spines were studied. Age- and component-related developmental anatomical features included variations in the ossification centers, cartilages, growth plates, vertebral centrum, facet joints, and annular fibers and nucleus pulposus of the intervertebral discs. The flexibility responses of the models were determined under pure compression, pure flexion, pure extension, and varying degrees of combined compression–flexion and compression–extension. The pediatric spine responses obtained with the pure overall (only geometric) scaling of the adult spine indicated that the flexibilities consistently increase in a uniform manner from six- to one-year-old spines under all loading cases. In contrast, incorporation of local anatomic changes specific to the pediatric spines of the three age groups (maintaining the same adult size) not only resulted in considerable increases in flexibilities, but the responses also varied as a function of the age of the pediatric spine and type of external loading. When the geometric scaling effects were added to these spines, the increases in flexibilities were slightly higher; however, the pattern of the responses remained the same as found in the previous approach. These results indicate that inclusion of developmental anatomical changes characteristic of the pediatric spines has more of a predominant effect on biomechanical responses than extrapolating responses of the adult spine based on pure overall geometric scaling. [S0148-0731(00)00501-X]
Vapor Phase Lubrication for Expendable Gas Turbine Engines
Authors: Wagner Matthew J. , Forster Nelson H. , Van Treuren Kenneth W. , Gerardi David T.
Published: July 2002

Vapor phase lubrication (VPL) is an emerging technology that is currently targeted for application in limited life, expendable engines. It has the potential to cut 90 percent of the cost and weight of the lubrication system, when compared to a conventional liquid lubricated system. VPL, is effective at much higher temperatures than conventional liquid lubrication (600°C versus 200°C), so considerably less cooling for the bearing is required, to the extent that the bearing materials often dictate the maximum upper temperature for its use. The hot no. 8 bearing and the cold no. 1 bearing of the T63 engine were used to evaluate the applicability of this technology to the expendable engine environment. The no. 8 bearing was a custom made hybrid with T15 steel races, silicon nitride balls, and a carbon–carbon composite cage; it was run for 10.7 h at a race temperature of 450°C at full power, without incident. Prior to engine tests, a bearing rig test of the no. 8 bearing demonstrated an 18.6 h life at a race temperature of 500°C at engine full power speed of 50,000 rpm. Cold bearing performance was tested with the standard no. 1 bearing, which consisted of 52100 steel races and balls, and a bronze cage; it was run for 7.5 h at a race temperature of 34°C at flight idle power, without incident. A self-contained lubricant misting system, running off compressor bleed air, provided lubricant at flow rates of 7–25 ml/h, depending on engine operating conditions. These tests have demonstrated for the first time that a single self-contained VPL system can provide adequate lubrication to both the hot and cold bearings for the required life of an expendable cruise missile engine. [S0742-4795(00)01302-2]
Study of a Novel Squeeze Film Damper and Vibration Generator
Authors: Suciu C. V. , Bonneau O. , Brun-Picard D. , Fre^ne J. , Pascovici M. D.
Published: July 2002

A novel squeeze film damper and vibration generator (SFD&VG) is proposed as an option in the vibration control field. The SFD&VG can be used as an active squeeze film damper (ASFD) or as a vibration generator (vibrator), for unidimensional vibration damping or generation. The SFD&VG concept is connected with current research to improve a common industrial process—drilling of deep holes. The SFD&VG is based on the variable area of the lubricant film, which allows the development of a variable force, and a change in fluid film stiffness and damping. The analysis is initiated for an elementary configuration of the SFD&VG—the infinite width Rayleigh step case—and then it is developed for an advanced elliptical SFD&VG. The Reynolds equation is solved for both pure squeeze film effect which provides vibration damping, and pure hydrodynamic wedge effect which provides vibration generation. The theoretical part is continued with the SFD&VG dynamic simulation. The SFD&VG experimental device and vibration measurements, performed for the two defined regimes, ASFD and vibration generator, are presented. Finally, the experimental and theoretical results are briefly compared. [S0742-4787(00)05201-2]
Friction Reduction in the Sliding of an Elastic Half-Space Against a Rigid Surface Due to Incident Rectangular Dilatational Waves
Authors: Adams George G.
Published: July 2002

The steady sliding of a flat homogeneous and isotropic elastic half-space against a flat rigid surface, under the influence of incident plane dilatational waves, is investigated. The interfacial coefficient of friction is constant with no distinction between static and kinetic friction. It is shown here that the reflection of a harmonic wave under steady sliding consists of a pair of body waves (a plane dilatational wave and a plane shear wave) radiated from the sliding interface. Each wave propagates at a different angle such that the trace velocities along the interface are equal and supersonic. The angles of wave propagation are determined by the angle of the incident wave, by the Poisson’s ratio, and by the coefficient of friction. The amplitude of the incident waves is subject only to the restriction that the perturbations in interface contact pressure and tangential velocity satisfy the inequality constraints for unilateral sliding contact. It is also found that an incident rectangular wave can allow for relative sliding motion of the two bodies with a ratio of remote shear to normal stress which is less than the coefficient of friction. Thus the apparent coefficient of friction is less than the interface coefficient of friction. This reduction in friction is due to periodic stick zones which propagate supersonically along the interface. The influences of the angle, amplitude, and shape of the incident rectangular wave, the interfacial friction coefficient, the sliding speed, and of the remotely applied normal stress, on friction reduction are determined. Under appropriate conditions, the bodies can move tangentially with respect to each other in the absence of an applied shear stress. [S0742-4787(00)00201-0]
Film growth precursors in a remote SiH4 plasma used for high-rate deposition of hydrogenated amorphous silicon
Authors: Kessels W. M. M. , van de Sanden M. C. M. , Schram D. C.
Published: July 2002

The SiH4 dissociation products and their contribution to hydrogenated amorphous silicon (a-Si:H) film growth have been investigated in a remote Ar–H2–SiH4 plasma which is capable of depositing device-quality a-Si:H at 10 nm/s. SiH3 radicals have been detected by means of threshold ionization mass spectrometry for different fractions of H2 in the Ar–H2-operated plasma source. It is shown that at high-H2 flows, SiH4 dissociation is dominated by hydrogen abstraction and that SiH3 contributes dominantly to film growth. At low-H2 flows, a significant amount of very reactive silane radicals, SiHx(x⩽2), is produced, as concluded from threshold ionization mass spectrometry on SiH2 and optical emission spectroscopy on excited SiH and Si. These radicals are created by dissociative recombination reactions of silane ions with electrons and they, or their products after reacting with SiH4, make a large contribution to film growth at low-H2 flows. This is corroborated by the overall surface reaction probability which decreases from ∼0.5 to ∼0.3 with increasing H2 fraction. The film properties improve with increasing H2 flow and device-quality a-Si:H is obtained at high H2 fractions where SiH3 dominates film growth. Furthermore, it is shown that at high-H2 flows the contribution of SiH3 is independent of the SiH4 flow while the deposition rate varies over one order of magnitude.
Study of the fundamental contributions to line edge roughness in a 193 nm, top surface imaging system
Authors: Somervell Mark H. , Fryer David S. , Osborn Brian , Patterson Kyle , Byers Jeffrey , Willson C. Grant
Published: July 2002

Top surface imaging systems based on vapor phase silylation have been investigated for use at a variety of wavelengths. This approach to generating high aspect ratio, high resolution images held great promise particularly for 193 nm and EUV lithography applications. Several 193 nm top surface imaging (TSI) systems have been described that produce very high resolution (low k factor) images with wide process latitude. However, because of the line edge roughness associated with the final images, TSI systems have fallen from favor. In fact, TSI does not appear in the strategy or plan for any imaging technology at this time. Most of the 193 nm TSI systems that have been studied are based on poly(p-hydroxystyrene) resins. These polymers have an unfortunate combination of properties that limit their utility in this application. These limiting properties include (1) high optical density, (2) poor silylation contrast, and (3) low glass transition temperature of the silylated material. These shortcomings are related to inherent polymer characteristics and are responsible for the pronounced line edge roughness in the poly(p-hydroxystyrene) systems. We have synthesized certain alicyclic polymers that have higher transparency and higher glass transition temperatures. Using these polymers, we have demonstrated the ability to print high resolution features with very smooth sidewalls. This article describes the synthesis and characterization of the polymers, their application to top surface imaging at 193 nm, and the analysis that was used to tailor the processing and the polymer’s physical properties to achieve optimum imaging.
Vapor-phase grown chalcogenide glass layers: An evaluation of their optical constants
Authors: Tick P. A. , Wallace N. W. , Teter M. P.
Published: July 2002

A new method of depositing amorphous chalcogenide glass layers by chemical vapor deposition has been developed. It was demonstrated that thicknesses up to 1 μ of compositions in the Si–As–Te system could be deposited on sapphire substrates. The optical constants of these layers were measured in the 2 to 5-μ region and indices of refraction between 3.4 and 3.6, with extinction coefficients less than about 0.02, were observed. One of the major advantages of this technique is that is does not require vacuum. The initial work on the Si–Te–As system resulted in layers which were macroscopically uniform with no apparent crystallinity. The capability of compositional grading is also inherent in the method and its application as a corrosion barrier is demonstrated.
The Optical Constants of CuO0.67 from 400 to 800 mμ
Authors: Czanderna A. W. , Boyko F. L.
Published: July 2002

At temperatures below 200 °C, copper films less than 1085 Å thick oxidize in 100 Torr of oxygen to form CuO0.67 before nucleation to CuO sets in. The oxidation of copper to CuO0.67 can be described by two parallel absorbing layers. During the oxidation, the transmittance, T, at normal incidence has been measured as a function of the wavelength λ while the mass change of the copper film has been simultaneously recorded with a vacuum ultramicrobalance. The thickness of the two absorbing layers, d1 and d2, has been calculated from the mass data. Using the measured values of T, λ, d1, and d2 and known values for the optical constants, n and k, for annealed copper films, trial values for n and k for the oxide have been inserted into rigorously derived equations for two parallel homogeneous absorbing films on a nonabsorbing substrate. By comparing the values of the transmittance calculated by a computer with the experimental values, k–n pairs are found that yield the measured transmittance. When the k–n pairs are plotted for several thickness combinations, a unique set of n and k is determined from the convergence or clustering of the n and k curves in a narrow region. Each set of n and k has a variable percentage error associated with it at any wavelength depending on how closely the curves cluster when they are plotted in the k–n plane. A narrow range of values of n and k are reported for CuO0.67 layers on copper in 50-mμ intervals for 400 to 800 mμ. The values reported are valid for oxide thicknesses exceeding about 800 Å.
A Quantitative Study of Auger Electron Signals of Phosphorus on Silicon Using a Quartz Crystal Microbalance
Authors: Levenson L. L. , Davis L. E. , Bryson C. E. , Melles J. J. , Kou W. H.
Published: July 2002

The Auger electron intensities of phosphorus on the (111) face of silicon have been measured as a function of coverage. Measurements of phosphorus coverage were obtained by using a quartz crystal microbalance during phosphorus (P2) evaporation from gallium phosphide crystals. A mass spectrometer was used to determine sticking coefficients on both the microbalance and sample.
Sub-0.1 μ electron-beam lithography for nanostructure development
Authors: Peckerar Martin , Bass Robert , Rhee Kee Woo
Published: July 2002

This article discusses those factors that lead to resolvability in e-beam lithography. The primary tool of study is the simplex method of linear optimization theory. Resist exposure characteristics can effectively be accounted for using a “minimum contrast” approach. The simplex exposure technique does not require exposure in the normally unexposed field. Feature linearity comparison experiments and boundary placement studies show measurable improvement with simplex when compared to dose scaling or feature boundary resizing. While computational tractability is a significant issue, the technique will rapidly assess whether small groups of features are resolvable. In addition, simplex points to general rules for applying dose modulation to different classes of features.
Comparison of resist collapse properties for deep ultraviolet and 193 nm resist platforms
Authors: Cao Heidi B. , Nealey Paul F. , Domke Wolf-Dieter
Published: July 2002

A comparison of collapse behavior was made for photoresist features with linewidths from 80 to 200 nm, spacing from 100 to 350 nm, and aspect ratios from 2 to 6 for four different resist platforms: acrylic based resists, acrylic resists based upon the Fujitsu platform, cyclo-olefin–maleic anhydride based resists, and Apex E, a poly(hydroxystyrene) based resist. The percentage of collapse for different gratings was determined using top-down scanning electron microscope images. A methodology was introduced to compare collapse properties between platforms by determining the critical aspect ratio of collapse (CARC) as a function of spacing between resist structures. We demonstrated the validity of this approach using an extensive set of statistically significant data for Apex E, and we determined that the CARC decreased linearly as the spacing between lines of resist decreased. The physical origin of the approach was discussed in terms of the mechanics of beam bending and the thermodynamics of surface tension. The methodology was applied to limited data sets for other resist platforms. The four resist platforms exhibited different values of CARC at constant spacing and a different dependence of CARC as a function of spacing. Resist performance in terms of collapse properties was ranked in the following order: cyclo-olefin–maleic anhydride resists > poly(hydroxystyrene) resist and acrylic resists based on the Fujitsu platform > acrylic resists.
Nature of oxygen at rocksalt and spinel oxide surfaces
Authors: Langell M. A. , Kim J. G. , Pugmire D. L. , McCarroll W.
Published: July 2002

The chemical environment of oxygen in cobalt-containing metal oxides with compositions MxM(x−1)′O and MxM(3x−1)′O4 (M,M′=Mn,Ni,Co) has been studied by Auger, x-ray and ultraviolet photoelectron, and high resolution electron energy loss spectroscopies. While there is a single type of lattice oxygen in the bulk structure of simple rocksalt and spinel oxides, the nature of oxygen at the surface of the spinel oxides is considerably more complex. Photoemission from core oxygen states in these materials often shows multiple peaks and satellite structure which have been attributed to a range of intrinsic and extrinsic oxygen states. All of these 3d transition metal oxides show a single, intense O 1s core photoemission peak at approximately 529.6 eV. In the spinel materials, a second state at 531.2 eV is also observed and is shown to be intrinsic to the spinel surface and not a result of hydroxylation or other surface contaminant. Similar photoemission features in Fe3O4 were previously attributed to final state effects; however, the nature of the multiple final states remains to be elucidated.
Diamond emitter arrays with uniform self-aligned gate built from silicon-on-insulator wafer
Authors: Wisitsora-at A. , Kang W. P. , Davidson J. L. , Kerns D. V. , Kerns S. E.
Published: July 2002

A self-aligned gate fabrication technique utilizing silicon-on-insulator technology is developed for the fabrication of large uniform arrays of diamond field emitters with self-aligned gate and sharp tip cathode. A uniform array with millions of gated diamond microemitters was reproducibly achieved. The diamond field emitter array, tested in triode configuration with an external anode, has a low turn-on gate voltage of 26 V. A high emission current of 1 μA per tip was obtained at a gate voltage of approximately 60 V and an anode voltage of 200 V. The ability to modulate emission current at low gate voltage allows more practical usage of a diamond field emitter in vacuum microelectronics.
Determination of the indices of refraction of molecular-beam-epitaxy-grown ZnSe/ZnCdSe multiple-quantum-well structures
Authors: Peiris F. C. , Bindley U. , Furdyna J. K.
Published: July 2002

We have fabricated a series of ZnSe/ZnCdSe multiple-quantum-well (MQW) structures in order to test the dependence of the resultant index of refraction n of the composite system on the n values of the constituents. The ZnSe/ZnCdSe MQWs were grown by molecular-beam epitaxy on GaAs substrates. We used photoluminescence and x-ray diffraction experiments to initially characterize the specimens. Using a prism coupler system—which measures n with high precision—we obtained n at three discrete laser wavelengths. We find that the effective values of n of these MQWs differ from their “Vegard-law-like” values; that is, the n of the composite structure is not a linear function of the n values of the constituents. This departure results from the energy-level structure of the MQW system associated with confinement of electrons and holes in the well layers.
Two-dimensional pulsed-plasma simulation of a chlorine discharge
Authors: Ramamurthi Badri , Economou Demetre J.
Published: July 2002

A two-dimensional (r,z) continuum model was developed to study the spatiotemporal dynamics of a pulsed power (square-wave modulated) chlorine discharge sustained in an inductively coupled plasma (ICP) reactor with a planar coil. The self-consistent model included Maxwell’s equations for the power deposition profiles coupled to the electron energy equation and the species mass balances. Simulation results showed separation of the plasma into an electronegative core and an electropositive edge during the active glow (power on) and the formation of an ion–ion plasma ∼15 μs into the afterglow (power off). During the early active glow, the negative ion flux was convection dominated near the quartz window of the ICP reactor due to the formation of large electrostatic fields, leading to a self-sharpening front propagating into the plasma. The negative ion density profiles were found to have a strong spatial dependence underlying the importance of spatial resolution in negative ion density measurements. The time dependent ion and radical flux uniformity was also studied. Simulation results were compared with experimental data and reasonable agreement was observed.