bluuebunny/crossref_metadata_2025 huggingface dataset:
Active Steering Control Based on the Estimated Tire Forces
Authors: Huh Kunsoo , Kim Joonyoung
Published: July 2002

Steered vehicles on slippery roads tend to slide outward with less lateral force than on high friction roads. In this paper, an active steering control method is proposed such that the vehicles on slippery roads are steered as if they are driven on high friction roads. In order to estimate the lateral force at each tire, a monitoring model is developed utilizing not only the vehicle dynamics but also the roll motion. The estimated lateral force is compared with the optimal reference force and the difference is compensated by the active steering controller. A fuzzy logic rule is designed for the active controller and its performance is evaluated on a steering Hardware-In-the-Loop Simulation (HILS) system. Steering results on slippery curved and sinusoidal roads demonstrate the effectiveness of the proposed controller. The drivers with the controller can steer the vehicles as if they are always driving on the high friction road, because the deviation from the high friction road is accommodated by the proposed steering controller. This method can be realized with the steer-by-wire concept and is promising as an active safety technology.
Numerical Analysis of Thermal Stratification in a Circular Pipe
Authors: Jo Jong Chull , Kim Yun Il , Choi Seok Ki
Published: July 2002

This paper presents an effective numerical method for predicting the stratified flow in a horizontal circular pipe. The method employs a body-fitted, nonorthogonal grid system to accommodate the pipe wall of circular geometry and the interface of the two fluids at different temperatures, of which the level is variable. The transient behaviors of fluid flow and temperature distribution in the piping are simulated using the finite volume approach. The convection term is approximated by a higher-order bounded scheme named HLPA, which is known as a high-resolution and bounded discretization scheme. The cell-centered, nonstaggered grid arrangement is adopted and the resulting checkerboard pressure oscillation is prevented by the application of modified momentum interpolation scheme. The SIMPLE algorithm is employed for the pressure and velocity coupling. The new way of treating the unsteady conjugate heat transfer problem is presented. The present method has been applied to the stratified flow in the pressurizer surge line of the nuclear reactor, and the results have been discussed. In addition, this study has investigated the effects of level of the interface between the two stratified fluids on the transient evolution of temperature distributions in the piping wall.
Adaptive Control of Active Balancing Systems for Speed-Varying Rotors Using Feedforward Gain Adaptation Technique
Authors: Shin Kwang-Keun , Ni Jun
Published: July 2002

This paper presents a new adaptive control method for active balancing of speed-varying rotors. It is developed based on the feedforward gain adaptation problem, which is a classical technique in the continuous-time adaptive control area. The condition for using this technique is the need for strictly positive realness of the transfer function. In this research, the technique is re-examined and modified to be appropriate for the balancing problem. It is also shown that the rotor dynamics of single-plane balancing problem can easily be converted to a strictly positive real transfer function and that, consequently, the feedfoward gain adaptation technique can be applied. This paper demonstrates that the developed method can be applied to a simple Jeffcott rotor and can also be extended to the single-plane balancing problem of general flexible rotor. Simulation studies show that the new method works well as expected.
Jet Impingement Boiling From a Circular Free-Surface Jet During Quenching: Part 1—Single-Phase Jet
Authors: Hall David E. , Incropera Frank P. , Viskanta Raymond
Published: July 2002

This paper reports results from an experimental study of boiling heat transfer during quenching of a cylindrical copper disk by a subcooled, circular, free-surface water jet. The disk was heated to approximately 650°C, and as quenching occurred, transient temperature measurements were taken at discrete locations near the surface and applied as boundary conditions in a conduction model to deduce transient heat flux distributions at the surface. Results are presented in the form of heat flux distributions and boiling curves for radial locations varying from the stagnation point to ten nozzle diameters for jet velocities between 2.0 and 4.0 m/s 11,300⩽Red⩽22,600. Data for nucleate boiling in the stagnation region and spatial distributions of maximum heat flux are presented and are in good agreement with correlations developed from steady-state experiments. Spatial distributions of minimum film boiling temperatures and heat fluxes are also reported and reveal a fundamental dependence on jet deflection and streamwise location. A companion paper (Hall et al., 2001) describes single-phase and boiling heat transfer measurements from a two-phase (water-air), free-surface, circular jet produced by injecting air bubbles into the jet upstream of the nozzle exit.
Static Friction Modeling in the Presence of Soft Thin Metallic Films
Authors: Liu Zhiqiang , Neville Anne , Reuben R. L.
Published: July 2002

A numerical model is presented for computing the static friction coefficient of rough surfaces with a soft thin film. In the calculation, an improved model, based on that due to Derjaguin et al., is used in conjunction with an elastic-plastic contact model for contact with a soft coating. The effects of the film thickness and surface roughness on the static friction coefficient and contact are investigated. The numerical results reflect published experimental observations and show the static friction coefficient depends strongly on surface film thickness, external force and surface roughness. The static friction coefficient (μ) increases with the surface film thickness when the plasticity index ψ⩾0.5 whilst μ increases with decreasing film thickness in the very thin film regime when ψ=0.25 and F/AnE<10−4. For real rough surfaces, contact and friction behavior is probably heavily influenced by the existence of such soft, thin surface films, which increase the contact area due to plastic deformation of the film and the contact stiffness of the surface in the case of thin film and light load.
Real-Time Process Characterization of Open Die Forging for Adaptive Control
Authors: Nye T. J. , Elbadan A. M. , Bone G. M.
Published: July 2002

Open die forging is a process in which products are made through repeated, incremental plastic deformations of a workpiece. Typically, the workpiece is held by a manipulator, which can position the workpiece through program control between the dies of a press. The part programs are generated with an empirically derived parameter, called the spread coefficient, whose value is subject to some contention. In this work, we demonstrate how process information can be used in real time to derive the actual spread coefficient for a given workpiece as it is being formed. These measurements and calculations occur in real time, and can be used to regenerate part programs to optimize the forming process, or can be used to adaptively control each incremental deformation of the workpiece.
Process Optimal Design in Forging by Genetic Algorithm
Authors: Chung J. S. , Hwang S. M.
Published: July 2002

A genetic algorithm based approach is presented for process optimal design in forging. In this approach, the optimal design problem is formulated on the basis of the integrated thermo-mechanical finite element process model so as to cover diverse design variables and objective functions, and a genetic algorithm is adopted for conducting design iteration for optimization. The process model, the formulation for process optimal design, and the genetic algorithm are described in detail. The approach is applied to several selected process design problems in cold and hot forging.
Three-Dimensional Field Equations of Motion, and Energy Functionals for Thick Shells of Revolution With Arbitrary Curvature and Variable Thickness
Authors: Kang J.-H. , Leissa A. W.
Published: July 2002

Equations of motion and energy functionals are derived for a three-dimensional coordinate system especially useful for analyzing the static and dynamic behavior of arbitrarily thick shells of revolution having variable thickness. The field equations are utilized to express them in terms of displacement components.
Experimental Investigation of a Highly Skewed Propeller in Ice
Authors: Searle Shawn , Veitch Brian , Bose Neil
Published: July 2002

Ice tank experiments done to investigate the interaction of a highly skewed propeller with ice are described. An introduction to propeller-ice interaction, the test setup, and the main results from the work are presented. The test matrix was designed to investigate the effect of variations in ice cut depth and advance ratio on propeller shaft thrust and torque. The results are discussed in terms of design strength requirements for highly skewed propellers operating in ice.
Heat Transfer Associated to Natural Convection Flow in a Partly Porous Cavity
Authors: Mercier Jean-Franc¸ois , Weisman Catherine , Firdaouss Mouaouia , Le Que´re´ Patrick
Published: July 2002

The object of this study is the heat transfer associated to a buoyancy-induced flow developing in a rectangular cavity, partly filled with porous medium, with given heat flux from the sides. Numerical experiments show the existence of a quasi parallel solution away from the top and bottom end walls, characterized by a linear vertical temperature profile. Analytical expressions are derived for the velocity and temperature which, combined with an energy balance, enable us to relate the stratification to the other governing parameters. Influence of the porous layer’s permeability and width, and of the Rayleigh number on the flow structure and heat transfer is thoroughly investigated, and summarized in simple relationships.
Prediction of Grain-Boundary Interfacial Mechanisms in Polycrystalline Materials
Authors: Ashmawi W. M. , Zikry M. A.
Published: July 2002

A multiple slip dislocation-density based crystalline formulation has been coupled to a kinematically based scheme that accounts for grain-boundary (GB) interfacial interactions with dislocation densities. Specialized finite-element formulations have been used to gain detailed understanding of the initiation and evolution of large inelastic deformation modes due to mechanisms that can result from dislocation-density pile-ups at GB interfaces, partial and total dislocation-density transmission from one grain to neighboring grains, and dislocation density absorption within GBs. These formulations provide a methodology that can be used to understand how interactions at the GB interface scale affect overall macroscopic behavior at different inelastic stages of deformation for polycrystalline aggregates due to the interrelated effects of GB orientations, the evolution of mobile and immobile dislocation-densities, slip system orientation, strain hardening, geometrical softening, geometric slip compatibility, and localized plastic strains. Criteria have been developed to identify and monitor the initiation and evolution of multiple regions where dislocation pile-ups at GBs, or partial and total dislocation density transmission through the GB, or absorption within the GB can occur. It is shown that the accurate prediction of these mechanisms is essential to understanding how interactions at GB interfaces affect and control overall material behavior.
Deformation and Bending Stress Analysis of a Three-dimensional, Thin-rimmed Gear
Authors: Li Shuting
Published: July 2002

This paper analyzed the deformations and bending stresses of a three-dimensional (3D), thin-rimmed gear (TRG) through using the finite element method (FEM) and a whole gear deformation model. The gear’s deformations and stresses at every part are analyzed in detail. In contrast with tooth bending deformations of a solid gear, 3D-TRG has not only tooth bending deformations, but also rim and web bending deformations. This paper found that the thin rim and web share about 70% deformations in the total deformations of the 3D-TRG and the gear tooth share only about 30%. It is also pointed out by this paper that not only the root stresses of the 3D-TRG are much greater than the solid gear because of the rim and web deformations, but also there are much greater stresses existing in the joint of the thin rim and the web. Especially, when the rim thickness becomes very thin, stresses at the joint shall become much greater than the root stresses. It is very necessary to regard the joint as the second critical stress point as well as the tooth root when to design 3D-TRG.
Numerical Prediction of Hot-Wire Corrections Near Walls
Authors: Durst Franz , Shi Jun-Mei , Breuer Michael
Published: July 2002

A thorough numerical investigation was performed for the two-dimensional convective heat transfer of a circular cylinder in a Couette flow close to a wall in order to study the hot-wire near-wall correction. A finite-volume Navier-Stokes solver enhanced by local block refinement and multigrid acceleration guaranteed highly accurate and efficient computational results. Unlike all previous numerical simulations, a more realistic model was used in the present study by taking the heat transfer in the solid wall into account to bridge the discrepancy between the previous theoretical models and the real situation. The computed results from the present investigation show good agreement with experimental data in the literature. Reference correction curves for hot-wire anemometers with respect to different wall materials (e.g., aluminum, glass, Perspex, air, etc.) were obtained.
Nonlinear Dynamic Model of a Two-Stage Pressure Relief Valve for Designers
Authors: Zung Pei-Sun , Perng Ming-Hwei
Published: July 2002

This paper presents a handy nonlinear dynamic model for the design of a two stage pilot pressure relief servo-valve. Previous surveys indicate that the performance of existing control valves has been limited by the lack of an accurate dynamic model. However, most of the existing dynamic models of pressure relief valves are developed for the selection of a suitable valve for a hydraulic system, and assume model parameters which are not directly controllable during the manufacturing process. As a result, such models are less useful for a manufacturer eager to improve the performance of a pressure valve. In contrast, model parameters in the present approach have been limited to dimensions measurable from the blue prints of the valve such that a specific design can be evaluated by simulation before actually manufacturing the valve. Moreover, the resultant model shows excellent agreement with experiments in a wide range of operating conditions.
Ultrafast Deformation in Femtosecond Laser Heating
Authors: Tzou D. Y. , Beraun J. E. , Chen J. K.
Published: July 2002

The hot-electron blasting model is extended in this work to describe the ultrafast deformation in thin metal films during the sub-picosecond to picosecond domain. The driving force exerting on the cold metal lattices is induced by the highly heated electrons, dictated by both the temperature and temperature gradient established in the hot electron during the picosecond transient. Since the metal lattices remain almost thermally undisturbed in this highly non-equilibrium regime, the resulting ultrafast deformation patterns cannot be described by the classical dynamical theory of thermoelasticity. The phonon-electron interaction model is used to describe the electron temperature and hence the driving force. The dominating parameters characterizing the nonlinearly coupled ultrafast heating and deformation are identified. Method of lines is used to solve the coupled field equations describing ultrafast deformation in the picosecond domain.
Effects of Shot-Peening on Fretting-Fatigue Behavior of Ti-6Al-4V
Authors: Namjoshi S. A. , Jain V. K. , Mall S.
Published: July 2002

The effects of shot-peening on the fretting fatigue behavior of titanium alloy, Ti-6Al-4V were investigated. Specimens were shot-peened as per AMS 2432 standard. X-ray diffraction analysis measured a maximum compressive stress of 800 MPa at the specimen surface, which reduced to zero at a depth of 188 μm. The compensatory residual tensile stress in the specimen was estimated using a curve fitting technique, the maximum value of which was found to be 260 MPa at a depth of 255 μm. Fretting fatigue tests were conducted at room temperature at a cyclic frequency of 200 Hz. Scanning electron microscopy of the shot-peened fretting fatigue specimens showed that the crack initiated at a point below the contact surface, the depth of which was in the range of 200–300 μm. Finite element analysis of the fretting fatigue specimens was also conducted. Fatigue life diagrams were established for the fretting fatigue specimens with and without shot-peening, and were compared to those under the plain fatigue condition, i.e. without fretting. Shot-peening improved the fretting fatigue life of Ti-6Al-4V; furthermore, it moved the crack initiation site from the fretting contact region to a region inside the specimen. Moreover, stress analysis showed that the fatigue failure of shot-peened specimens was caused by the compensatory tensile residual stress.
Reliable Real-Time Solution of Parametrized Partial Differential Equations: Reduced-Basis Output Bound Methods
Authors: Prud’homme C. , Rovas D. V. , Veroy K. , Machiels L. , Maday Y. , Patera A. T. , Turinici G.
Published: July 2002

We present a technique for the rapid and reliable prediction of linear-functional outputs of elliptic (and parabolic) partial differential equations with affine parameter dependence. The essential components are (i) (provably) rapidly convergent global reduced-basis approximations—Galerkin projection onto a space WN spanned by solutions of the governing partial differential equation at N selected points in parameter space; (ii) a posteriori error estimation—relaxations of the error-residual equation that provide inexpensive yet sharp and rigorous bounds for the error in the outputs of interest; and (iii) off-line/on-line computational procedures methods which decouple the generation and projection stages of the approximation process. The operation count for the on-line stage in which, given a new parameter value, we calculate the output of interest and associated error bound, depends only on N (typically very small) and the parametric complexity of the problem; the method is thus ideally suited for the repeated and rapid evaluations required in the context of parameter estimation, design, optimization, and real-time control.
Effect of Annular Incision Type on the Change in Biomechanical Properties in a Herniated Lumbar Intervertebral Disc
Authors: Natarajan R. N. , Andersson G. B. J. , Patwardhan A. G. , Verma S.
Published: July 2002

The technique used to incise the disc during discectomy may play a role in the subsequent healing and change in biomechanical stiffness of the disc. Several techniques of lumbar disc annulotomy have been described in clinical reports. The purpose of this paper was to study the influence of annulotomy technique on motion segment stiffness using a finite element model. Four incision methods (square, circular, cross, and slit) were compared. The analyses showed that each of the annular incisions produced increase in motions under axial moment loadings with circular incision producing the largest change in the corresponding rotational motion. Under shear loading mode, cross and slit-type annular incisions produced slightly larger changes in the principal motions of the disc than square and circular incisions. All other incision types considered in the current study produced negligibly small increase in motion under rest of the loading conditions. In addition to annulotomy, when nucleotomy was also included in the analyses, once again cross and slit incisions produced larger change in motion under shear loading mode as compared to the other two incision types. A comparison between the four types of annular incisions showed that cross incision produced an increase in motion larger than those produced by the other three incisions under flexion/extension and lateral moment loading and both shear force loadings. Circular incision produced the largest increase in motion under axial moment load in comparison to those produced by square, cross, and slit incisions. Sagittal plane symmetry was influenced by the incision injury to the motion segment leading to coupled motions as well as increased facet loads. From the study it can be concluded that the increase in flexibility of the disc due to annulotomy depends on the type of annulotomy, and the annulotomy also produce asymmetrical deformations leading to increased facet loading.
Turbine Engine Performance Improvements—A Proactive Approach
Authors: Gastineau Zane D.
Published: July 2002

Turbine engine concepts for the future are placing ever increasing demands on the design engineer. These future systems are seeking to increase performance while at the same time reduce costs. However, traditional engine design methods use large margins in the design process of a specific component in order to guarantee proper operation throughout the flight envelope over the life of the engine. These margins in fact reduce engine performance and increase the costs. In this paper, active control will be presented as one potential means of achieving the requirements for future turbine engines. In addition, specific active control applications will be discussed.
Characteristics of MCrAlY Coatings Sprayed by High Velocity Oxygen-Fuel Spraying System
Authors: Itoh Y. , Saitoh M. , Tamura M.
Published: July 2002

High velocity oxygen-fuel (HVOF) spraying system in open air has been established for producing the coatings that are extremely clean and dense. It is thought that the HVOF sprayed MCrAlY (M is Fe, Ni and/or Co) coatings can be applied to provide resistance against oxidation and corrosion to the hot parts of gas turbines. Also, it is well known that the thicker coatings can be sprayed in comparison with any other thermal spraying systems due to improved residual stresses. However, thermal and mechanical properties of HVOF coatings have not been clarified. Especially, the characteristics of residual stress, that are the most important property from the view point of production technique, have not been made clear. In this paper, the mechanical properties of HVOF sprayed MCrAlY coatings were measured in both the case of as-sprayed and heat-treated coatings in comparison with a vacuum plasma sprayed MCrAlY coatings. It was confirmed that the mechanical properties of HVOF sprayed MCrAlY coatings could be improved by a diffusion heat treatment to equate the vacuum plasma sprayed MCrAlY coatings. Also, the residual stress characteristics were analyzed using a deflection measurement technique and a X-ray technique. The residual stress of HVOF coating was reduced by the shot-peening effect comparable to that of a plasma spray system in open air. This phenomena could be explained by the reason that the HVOF sprayed MCrAlY coating was built up by poorly melted particles. [S0742-4795(00)00701-8]
High Temperature Oxidation and Corrosion of Silicon-Based Non-Oxide Ceramics
Authors: Klemm H. , Herrmann M. , Schubert C.
Published: July 2002

The present study is focussed on the oxidation behavior of nonoxide silicon-based ceramics. Various Si3N4 and SiC ceramics were examined after long term oxidation tests (up to 5000 h) at 1500°C in ambient air. The damage mechanisms were discussed on the basis of a comprehensive chemical and microstructural analysis of the materials after the oxidation tests. The diffusion of oxygen into the material and its further reaction in the bulk of the material were found to be the most critical factors during long term oxidation treatment at elevated temperatures. However, the resulting damage in the microstructure of the materials can be significantly reduced by purposeful microstructural engineering. Using Si3N4/SiC and Si3N4/MoSi2 composite materials provides the possibility to improve the high temperature stability. [S0742-4795(00)00301-X]
Channel Height Effect on Heat Transfer and Friction in a Dimpled Passage
Authors: Moon H. K. , O’Connell T. , Glezer B.
Published: July 2002

The heat transfer enhancement in cooling passages with dimpled (concavity imprinted) surface can be effective for use in heat exchangers and various hot section components (nozzle, blade, combustor liner, etc.), as it provides comparable heat transfer coefficients with considerably less pressure loss relative to protruding ribs. Heat transfer coefficients and friction factors were experimentally investigated in rectangular channels which had concavities (dimples) on one wall. The heat transfer coefficients were measured using a transient thermochromic liquid crystal technique. Relative channel heights H/d of 0.37, 0.74, 1.11, and 1.49 were investigated in a Reynolds number range from 12,000 to 60,000. The heat transfer enhancement NuHD on the dimpled wall was approximately constant at a value of 2.1 times that Nusm of a smooth channel over 0.37⩽H/d/⩽1.49 in the thermally developed region. The heat transfer enhancement ratio Nu¯HD/Nusm was invariant with Reynolds number. The friction factors (f) in the aerodynamically fully developed region were consistently measured to be around 0.0412 (only 1.6 to 2.0 times that of a smooth channel). The aerodynamic entry length was comparable to that of a typical turbulent flow xo/Dh=20, unlike the thermal entry length on dimpled surface which was much shorter xo/Dh<9.8. The thermal performance Nu¯HD/Nusm/f/fsm1/3≅1.75 of dimpled surface was superior to that 1.16<NuHD/Nusm/f/fsm1/3<1.60 of continuous ribs, demonstrating that the heat transfer enhancement with concavities can be achieved with a relatively low-pressure penalty. Neither the heat transfer coefficient distribution nor the friction factor exhibited a detectable effect of the channel height within the studied relative height range 0.37⩽H/d⩽1.49.[S0742-4795(00)02802-7]
Experimental Evaluation of a Metal Mesh Bearing Damper
Authors: Zarzour Mark , Vance John
Published: July 2002

Metal mesh is a commercially available material used in many applications including seals, heat shields, filters, gaskets, aircraft engine mounts, and vibration absorbers. This material has been tested by the authors as a bearing damper in a rotordynamic test rig. The test facility was originally used to support the design of a turboprop engine, developing squirrel cages and squeeze film dampers for both the gas generator and power turbine rotors. To design the metal mesh damper, static stiffness and dynamic rap test measurements were first made on metal mesh samples in a specially designed nonrotating test fixture. These property tests were performed on samples of various densities and press fits. One sample was also tested in an Instron machine as an ancillary and redundant way to determine the stiffness. Using the stiffness test results and equations derived by a previous investigator, a spreadsheet program was written and used to size metal mesh donuts that have the radial stiffness value required to replace the squirrel cage in the power turbine. The squirrel cage and squeeze film bearing damper developed for the power turbine rotor was then replaced by a metal mesh donut sized by the computer code. Coast down tests were conducted through the first critical speed of the power turbine. The results of the metal mesh tests are compared with those obtained from previous testing with the squeeze film damper and show that the metal mesh damper has the same damping as the squeeze film at room temperature but does not lose its damping at elevated temperatures up to 103°C. Experiments were run under several different conditions, including balanced rotor, unbalanced rotor, heated metal mesh, and wet (with oil) metal mesh. The creep, or sag, of the metal mesh supporting the rotor weight was also measured over a period of several weeks and found to be very small. Based on these tests, metal mesh dampers appear to be a viable and attractive substitute for squeeze film dampers in gas turbine engines. The advantages shown by these tests include less variation of damping with temperature, ability to handle large rotor unbalance, and the ability (if required) to operate effectively in an oil free environment. Additional testing is required to determine the endurance properties, the effect of high impact or maneuver loads, and the ability to sustain blade loss loads (which squeeze films cannot handle). [S0742-4795(00)01002-4]
Measurement of the Bubbly Flow Beneath Partial Attached Cavities Using Electrical Impedance Probes
Authors: George Darin L. , Iyer Claudia O. , Ceccio Steven L.
Published: July 2002

Surface electrical impedance probes are used to examine the bubbly flow beneath and in the closure region of partial attached cavities. A series of electrodes were mounted flush to the surface of a cavitating hydrofoil to detect the presence of liquid or vapor through changes in the impedance of the local fluid medium. Signals from the electrical probes were used to determine the near-surface gas-phase velocity and the shedding frequency of the gas phase. The impedance technique is shown to have the potential to measure advection velocities within a partial cavity, and the frequency content of the signal is used to determine the dynamics of the vapor shedding process. [S0098-2202(00)00501-0]
Turbulent Boundary Layers on Surfaces Covered With Filamentous Algae
Authors: Schultz Michael P.
Published: July 2002

Turbulent boundary layer measurements have been made on surfaces covered with filamentous marine algae. These experiments were conducted in a closed return water tunnel using a two-component, laser Doppler velocimeter (LDV). The mean velocity profiles and parameters, as well as the axial and wall-normal turbulence intensities and Reynolds shear stress, are compared with flows over smooth and sandgrain rough walls. Significant increases in the skin friction coefficient for the algae-covered surfaces were measured. The boundary layer and integral thickness length scales were also increased. The results indicate that profiles of the turbulence quantities for the smooth and sandgrain rough walls collapse when friction velocity and boundary layer thickness are used as normalizing parameters. The algae-covered surfaces, however, exhibited a significant increase in the wall-normal turbulence intensity and the Reynolds shear stress, with only a modest increase in the axial turbulence intensity. The peak in the Reynolds shear stress profiles for the algae surfaces corresponded to the maximum extent of outward movement of the algae filaments. [S0098-2202(00)01902-7]
Dynamic Characteristics of an In-Contact Headslider Considering Meniscus Force: Part 1—Formulation and Application to the Disk With Sinusoidal Undulation
Authors: Kato Takahisa , Watanabe Souta , Matsuoka Hiroshige
Published: July 2002

The authors present a three-degrees-of-freedom (3-DOF) model of an in-contact headslider/disk interface (HDI) system by which the dynamic characteristics of the in-contact headslider-suspension assembly can be obtained. Four regimes with respect to the interface of headslider and disk surface are shown to take the meniscus force of lubricant on the disk surface into account. The equations of motion of the in-contact headslider considering the meniscus force at each regime and the calculation results for the disk with sinusoidal undulation are described. [S0742-4787(00)01802-6]
UHV-Cleaved Single Crystal Ti2O3 (101¯2) by UPS and XPS
Authors: Kurtz Richard L. , Henrich V. E.
Published: July 2002

Ti2O3 is a semiconducting transition-metal oxide with a 0.1 eV bandgap at room temperature and is thus fairly conducting. The conducting nature of the oxide produces a double-peaked structure of the Ti 2p1/2 and 2p3/2 XPS core-level peaks. The sample, which exposes a (101¯2) cleavage face, contains only Ti3+ cations, so the double-peaked structure does not arise from the presence of multiple valence states on the Ti cations. Caution must thus be exercised in interpreting cation 3p core-level spectra from such oxides. [See K. E. Smith and V. E. Henrich, Phys. Rev. B 50, 1282 (1994) for a discussion of the role of final-state screening in XPS core-level line shapes. See also R. L. Kurtz and V. E. Henrich, Surf. Sci. Spectra 5, 172 (1998).] The He I and He II UPS spectra of the valence band region show the large O 2p band and the smaller Ti 3d band just below the Fermi level. The titanium oxides exhibit a wide stoichiometry range (including Magneli phases); Ti2O3 is the most stable lower oxide.
Formation of silicon nitride gate dielectric films at 300 °C employing radical chemical vapor deposition
Authors: Ohta Hiroyuki , Nagashima Atsushi , Ito Masafumi , Hori Masaru , Goto Toshio
Published: July 2002

Silicon nitride (SiNx) ultrathin gate dielectric films for ultralarge-scale integrated circuits have been successfully formed by radical chemical vapor deposition (R-CVD) at 300 °C. In this process, charged species incident on the silicon (Si) substrate during the growth were eliminated with the magnetic field in electron cyclotron resonance plasma-enhanced CVD employing nitrogen and silane (N2/SiH4) gases. By using R-CVD, SiNx films with very low leakage current and near-ideal dielectric constant (ε=7.2) have been obtained. In situ Fourier transform infrared reflection absorption spectroscopy (FT-IR RAS) has confirmed that the Si–N bonds are increased and the voids in films are reduced by eliminating charged species. A key factor for forming ultrathin SiNx films of high quality at 300 °C is discussed, based on characterization of films synthesized with and without charged species on the substrate using in situ x-ray photoelectron spectroscopy, in situ FT-IR RAS, and in situ atomic force microscopy.
Controlled ordering and positioning of InAs self-assembled quantum dots
Authors: Lee H. , Johnson J. A. , Speck J. S. , Petroff P. M.
Published: July 2002

An experimental approach has been developed to control the formation of InAs self-assembled islands. A lithographically defined mesa lattice on the surface was used to control the growth kinetics and island nucleation. Two distinct island formation regimes were observed from InAs islands grown on patterned GaAs (100) substrates. In the case of direct growth on patterned substrates, a type I islanding was observed, in which all the islands formed between mesas. Incorporating a stressor layer into the regrowth on the patterned substrate yielded a type island nucleation, where all the islands nucleated on top of the mesas. The possible mechanisms involved in the long range ordering and positioning of islands are discussed.
Near-surface chemistry in Zr2Fe and ZrVFe studied by means of x-ray photoemission spectroscopy: A temperature-dependent study
Authors: Kovac Janez , Sakho Oumar , Manini Paolo , Sancrotti M.
Published: July 2002

The near-surface atomic composition and the character of chemical bond in two nonevaporable gettering alloys have been investigated via core level (Zr 3d, Fe 2p, V 2p, O 1s, C 1s) photoemission. The samples have been measured in UHV after in-air fracturing and various annealing steps (up to 850 °C). For T>400 °C a progressive and sizeable decrease of the near surface C content along with an increase in the Zr concentration is observed in both alloys. An annealing induced Zr enrichment at the surface is found, the metallic atomic concentrations being significantly far from the nominal bulk stoichiometry. The annealing induces a strong evolution in the chemical bonds, the metallic species being completely oxidized in in-air fractured samples while a metallic character progressively emerges at increasing temperatures. Surface metallization proceeds faster in Zr2Fe than in the V-containing getter.
Electronic Conduction in Amorphous Semiconductors
Authors: Jonscher A. K.
Published: July 2002

A review is given of some electronic conduction processes in amorphous semiconductors and insulators. A detailed discussion is given of donorlike and traplike states in disordered solids and the various transitions between them are discussed in the context of low- and high-field conductivity under dc and ac conditions. Recent experimental and theoretical results are described relating to amorphous films of SiO, Ge, Si, and C. Some experimental results and theoretical interpretations of photoconductive studies on SiO are also given.
The Use of Graphite in High and Ultrahigh Vacuum: A Review
Authors: Beitel George A.
Published: July 2002

The state of the art of graphite technology as it pertains to high-vacuum technology has been reviewed. The review reveals that little is known about many of the vacuum properties of graphite, especially degassing characteristics in high vacuum, sticking probabilities, electronic desorption cross sections, sputtering yields, and x-ray production cross sections. The few existing studies which have used graphite in high or ultrahigh vacuum all indicate that, contrary to the popular opinion that graphite is a gassy material, when properly degassed, graphite remains more gas free than the metals commonly used in vacuum components. Specific uses of graphite in vacuum research are suggested. In particular, it is suggested that significant improvements can be achieved in the operation of vacuum gauges and residual gas analyzers by the use of graphite for the electrode material.
Diffusion in Thin Film Ti–Au, Ti–Pd, and Ti–Pt Couples
Authors: Tisone T. C. , Drobek J.
Published: July 2002

The interdiffusion and subsequent compound formation was investigated in thin film couples of Ti–Au, Ti–Pd, and Ti–Pt using transmission and glancing angle electron diffraction techniques. Aging temperatures up to 500°C and times up to 8 h were considered. For all three couples, intermetallic compound formation was observed in the as-deposited films indicating substantial diffusion during deposition (= 100–150°C). For the Ti–Au couples, the TiAu2, TiAu, and Ti3Au compounds formed during diffusion. For the Ti-Pd and Ti-Pt couples the isostructural compounds TiPd, TiPt and Ti3Pd, Ti3Pt were observed. After the formation of the Ti3Pd type compound diffusion ceased for temperatures <500°C indicating that this compound was acting as a diffusion barrier. In all cases Ti was found to be the fastest diffusing species, where it was observed that the diffusion occurred principally through the Au, Pd, or Pt grain boundaries. The effective diffusion coefficient was estimated to be about 105 times larger than expected for bulk diffusion. The role of diffusion in the formation of compounds and the role of film defects in determining the effective diffusion coefficients are discussed.
Step and flash imprint lithography: Template surface treatment and defect analysis
Authors: Bailey T. , Choi B. J. , Colburn M. , Meissl M. , Shaya S. , Ekerdt J. G. , Sreenivasan S. V. , Willson C. G.
Published: July 2002

We have finished the construction of an automated tool for step and flash imprint lithography. The tool was constructed to allow defect studies by making multiple imprints on a 200 mm wafer. The imprint templates for this study were treated with a low surface energy, self-assembled monolayer to ensure selective release at the template-etch barrier interface. This surface treatment is very durable and survives repeated imprints and multiple aggressive physical and chemical cleanings. The imprint and release forces were measured for a number of successive imprints, and did not change significantly. The process appears to be “self-cleaning.” Contamination on the template is entrained in the polymerizing liquid, and the number of defects is reduced with repeated imprints.
Electron cyclotron wave resonance plasma assisted deposition of cubic boron nitride thin films
Authors: Cao Z. X.
Published: July 2002

Cubic boron nitride (cBN) thin films have been deposited by sputtering the hexagonal boron nitride (hBN) target with nitrogen ions from a low-pressure plasma source. The electron-cyclotron-wave resonance (ECWR) plasma served both to sputter the hBN target and to simultaneously bombard the growing film. Deposits of over 90% cBN content were obtained with ion energies between 70 and 135 eV. The stoichiometry of the films was warranted by the extremely dense nitrogen ions arriving at the substrate. The frequency of the TO-mode for cBN on the Fourier-transform infrared (FTIR) spectra shifted up only slightly from the bulk value at 1065 cm−1. A maximum thickness of 350 nm for the cBN layer was achieved. A cross-sectional transmission electron microscopy (TEM) image showed that the film grew in the turbostratic boron nitride (tBN), aligned hBN-arrays and cBN sequence. At the hBN–cBN interface, some nanoarches were identified. The corresponding interplanar distances for the hBN (0002) and the cBN (111) planes are 0.321 and 0.212 nm, approximately ideal for the 2:3 lattice matching. Both the high-resolution TEM image and the arc pattern of the (111) reflection from selected-area electron diffraction revealed the textured structure of the cubic phase.
Damageless vacuum sealing of Si field emitters with CHF3 plasma treatment
Authors: Nagao M. , Matsukawa T. , Kanemaru S. , Itoh J. , Tanabe H.
Published: July 2002

Surface modification of Si field emitters by CHF3 plasma is investigated for damageless vacuum sealing. The emission characteristics of nontreated Si field emitters and CHF3-plasma-treated Si field emitters were measured in an ultra-high-vacuum chamber and in a frit-sealed vacuum package. The vacuum sealing process decreased the emission currents from the nontreated Si field emitters by a factor of 10. On the contrary, the emission current from the CHF3-plasma-treated emitters did not change before and after the vacuum sealing process. Analysis by Auger electron spectroscopy and by x-ray photoelectron spectroscopy revealed that the CHF3-plasma-exposed Si surface was covered with SiC and fluorocarbon films. These carbon-related films work as a protective material in the sealing process. By using this method, we achieved the first operation of metal–oxide–semiconductor field-effect-transistor-structured Si field emitters in a vacuum package.
Adatom assisted stabilization of ad dimers on Ge(001)
Authors: Zoethout E. , Zandvliet H. J. W. , Poelsema Bene
Published: July 2002

The early stage of silicon heteroepitaxial growth and germanium homoepitaxial growth on Ge(001) has caused a discrepancy between experimental and theoretical work. Previously a dimer configuration was identified experimentally, which theoretically has been predicted to be unfavorable: the D dimer. Upon careful reinvestigation this cluster turns out to be not a two-atom, but a three-atom cluster. The three-atom cluster of Ge or Si on Ge(001) is shown to differ from a C dimer, a small epitaxial island (BD) or the three-atom cluster of Si on Si(001).
Effect of film density on electrical properties of indium tin oxide films deposited by dc magnetron reactive sputtering
Authors: Choi S. K. , Lee J. I.
Published: July 2002

Tin-doped indium oxide (ITO) films were fabricated using dc magnetron reactive sputter deposition of an In 10 wt. % Sn alloy target in an Ar and O2 gas mixture. To understand the relationship between the electrical properties of ITO films and O2 partial pressure, the resistivity, carrier concentration and mobility, film density, and intrinsic stress in the films were measured as a function of O2 partial pressure. It was found experimentally that an ITO film having both maximum conductivity and carrier mobility has a film density close to its theoretical density. For the ITO film with density close to theoretical, the mean free path was the same as the grain size (=columnar diameter). This indicated that the electrical characteristics of the ITO films discussed here depend strongly on the grain size. However, for the ITO films with density lower than theoretical, the mean free paths were smaller than the grain size. It is suggested that electron scattering at pores and voids within the grain is the major obstacle for electron conduction in the ITO films having a lower density. The measurements of intrinsic stress indicate that the density of ITO films is determined by bombardment of oxygen neutrals on the growing film.
Interpretation of the Shirley background in x-ray photoelectron spectroscopy analysis
Authors: Castle J. E. , Salvi A. M.
Published: July 2002

This brief review sets out the facts concerning the intrinsic nature of the asymmetric background step associated with most peaks in an x-ray photoelectron spectroscopy spectrum. This step is most clearly seen if the extrinsic background is first subtracted by the methods suggested and developed by Tougaard. Recent work using synchrotron radiation has confirmed that the intrinsic loss tail is generated as a one-step process during photoemission and thus corresponds to a shakeup excitation to a continuum of final states. The background is useful in identifying compound formation and in some cases, can point to hybridization of the p and d orbitals. The review illustrates how the use of predetermined backgrounds gives advantages in curve fitting and concludes with a discussion of the impact of intrinsic losses on quantification.
Mobility enhancement by reduced remote impurity scattering in a pseudomorphic In0.7Ga0.3As/In0.52Al0.48As quantum well high electron mobility transistor structure with (411)A super-flat interfaces grown by molecular-beam epitaxy
Authors: Watanabe I. , Kanzaki K. , Aoki T. , Kitada T. , Shimomura S. , Hiyamizu S.
Published: July 2002

We have carried out a Shubnikov–de Haas (SdH) measurement at 4 K and investigated the electronic properties and scattering mechanisms in a pseudomorphic In0.7Ga0.3As/In0.52Al0.48As quantum well high electron mobility transistor (QW-HEMT) structure with a thin spacer thickness of 3 nm grown on a (411)A-oriented InP substrate by molecular-beam epitaxy (MBE). Electrons occupied the zeroth and first subbands in the 12-nm-thick In0.7Ga0.3As channel layer at two-dimensional electron gas (2DEG) densities of 3.10×1012 and 0.99×1012 cm−2, respectively. 2DEG mobilities of the (411)A sample for the zeroth and first subbands were μ0=52 000 and μ1=66 000 cm2/V s, which were much higher than those of the (100) QW-HEMT structure (μ0=22 000 and μ1=26 000 cm2/V s). The result indicates that the electron mobility of the (411)A sample is enhanced by reduction of remote impurity scattering because the spacer thickness (Lsp=3 nm) and distribution of sheet doped impurities are laterally uniform in the (411)A In0.7Ga0.3As/In0.52Al0.48As QW-HEMT structure.
Measurements of the critical inclusion size for arcing and macroparticle ejection from aluminum sputtering targets
Authors: Wickersham C. E. , Poole J. E. , Leybovich A. , Zhu L.
Published: July 2002

Arcing during sputtering is a significant cause of defect generation during sputter deposition of thin films. We studied the effect of dielectric inclusion size on the propensity for arcing while sputtering aluminum targets in argon at power densities ranging from 8 to near 60 W/cm2. We found that there is a critical inclusion size required for arcing to occur. The critical size for an Al2O3 inclusion in an aluminum-sputtering target in an argon plasma is 440±160 μm. Inclusions with sizes above this critical value readily induce arcing and macroparticle ejection during sputtering. Inclusions below this critical size do not cause arcing or macroparticle ejection. We also found that the inclusion critical size was not sensitive to the sputtering power density. When the inclusion size exceeds the critical value the plasma boundary over the inclusion is deformed by the charge accumulating on the dielectric inclusion and the plasma positive column diffuses toward the target leading to a bipolar arc. Inclusions below the critical size do not distort the dark space to an extent great enough to permit bipolar arc formation. Our proposed model predicts that the critical inclusion size depends upon the sheath thickness, which ranged between 300 and 600 μm for the experimental conditions used in this study.