bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of Bending Strength of Carburized Gears Based on a Quantification of Defect Size in the Surface Layer
Authors: Masuyama Tomoya , Kato Masana , Inoue Katsumi , Yamashita Toshihiko
Published: October 2002

Generally, fatigue strength of steel correlates with hardness up to a certain point. However, the relationship of hardness and fatigue strength is more complicated for high strength materials, mainly because strength is sensitive to material defects. This paper presents a determination of defect size in carburized gear teeth and a strength evaluation method based on that size. A micro notch is artificially processed at the fillet of carburized gear tooth by means of a Focused Ion Beam, and a bending fatigue test is performed. Threshold notch depth anth, the limit beyond which fatigue strength declines, is obtained by the test. Threshold notch depth is used as a measure to determine latent defect size in the surface layer. The anth of gears from which a nonmartensitic layer is removed by electro-polishing is shorter than the anth of gears with a nonmartensitic layer. The surface layer is observed by scanning electron microscope and electron probe micro analyzer to clarify latent defect characteristics. Many micro cracks, in addition to long cracks in the nonmartensitic layer, Cr oxides and Mn oxides near the surface, and Si segregated in grain boundary are observed. This demonstrates that they trigger fatigue crack initiation; and therefore defect size limits strength. Consequently, strength is expressed by an experimental formula of Vickers hardness and the square root of projected area of the defect obtained above.
An Analytic Methodology for the Kinematic Synthesis of Epicyclic Gear Mechanisms
Authors: Hsu Cheng-Ho
Published: October 2002

This paper presents an analytic method for the determination of the gear ratios of an epicyclic-type transmission mechanism for a given set of speed ratios. For the transmission mechanism with the associated clutching sequence table, the overall speed ratios are first derived and expressed in terms of the gear ratios of all the mating gears using the concept of fundamental geared entities. Next, the associated speed ratio relations are derived as a criterion to detect the feasibility of any given set of speed ratios. Finally, the transmission mechanism is decomposed into a system of fundamental geared entities such that the gear ratios of all the mating gears are determined from given speed ratios in an analytic way.
The Neural Network Position-Control of a Moving Platform Using Electrorheological Valves
Authors: Choi Seung-Bok , Sung Kum-Gil , Lee Jae-Wook
Published: October 2002

This paper presents position control of a moving platform using a hydraulic bridge circuit associated with electrorheological (ER) valves. Four cylindrical ER valves are designed and manufactured on the basis of electric field-dependent yield stress of an ER field, which is composed of chemically treated starch and silicone oil. The pressure drops of the ER valves are empirically identified with respect to the intensity of the electric field, and the hydraulic bridge circuit with four ER valves is constructed. The hydraulic cylinder system to be controlled by the ER valve bridge circuit is then incorporated with a moving platform of a cargo handling laboratory model. Subsequently, a neural network control scheme is formulated in order to control the position of the moving platform by activating ER valves of the cylinder system. The controller is experimentally realized and position tracking control results for desired trajectories of the moving platform are presented in the time domain.
Assessment of Mechanical Properties of Adherent Living Cells by Bead
Micromanipulation: Comparison of Magnetic Twisting Cytometry vs Optical Tweezers
Authors: Laurent Valérie M. , Hénon Sylvie , Planus Emmanuelle , Fodil Redouane , Balland Martial , Isabey Daniel , Gallet Franc¸ois
Published: October 2002

We compare the measurements of viscoelastic properties of adherent alveolar epithelial cells by two micromanipulation techniques: (i) magnetic twisting cytometry and (ii) optical tweezers, using microbeads of same size and similarly attached to F-actin. The values of equivalent Young modulus E, derived from linear viscoelasticity theory, become consistent when the degree of bead immersion in the cell is taken into account. E-values are smaller in (i) than in (ii): ∼34–58 Pa vs ∼29–258 Pa, probably because higher stress in (i) reinforces nonlinearity and cellular plasticity. Otherwise, similar relaxation time constants, around 2 s, suggest similar dissipative mechanisms.
Dynamic Redesign of a Flow Control Servovalve Using a Pressure Control Pilot1
Authors: Li Perry Y.
Published: October 2002

In this paper, the dynamic performance of an unconventional two-spool flow control servovalve using a pressure control pilot is analyzed. Such valves are less expensive than typical servovalves but also tend to be limited in their dynamic performance. Based on a previously developed eight state nonlinear model, we develop a simplified linear model which is able to capture the essential dynamics of the valve. Using root locus analysis method, the limitation in dynamic performance is shown to be due to a “zero” introduced by the structure of the interconnection of the subsystems. Design parameters that move the zero further to the left half plane, and do not adversely affect other steady-state criteria are identified. The effectiveness of these parameters to improve the dynamic performance is demonstrated. This analysis demonstrates how the structure of the interactions between subsystems in a dynamic component, such as a hydraulic valve, can critically limit the dynamic performance of the component.
Automated Design of Multi-Stage Molds for Manufacturing Multi-Material Objects
Authors: Kumar Malay , Gupta Satyandra K.
Published: October 2002

This paper describes a geometric algorithm for automated design of multi-stage molds for manufacturing multi-material objects. In multi-stage molding process, the desired multi-material object is produced by carrying out multiple molding operations in a sequence, adding one material in the target object in each mold-stage. We model multi-material objects as an assembly of single-material components. Each mold-stage can add only one type of material. Therefore, we need a sequence of mold-stages such that (1) each mold-stage only adds one single-material component either fully or partially, and (2) the molding sequence completely produces the desired object. In order to find a feasible mold-stage sequence, our algorithm decomposes the multi-material object into a number of homogeneous components to find a feasible sequence of homogeneous components that can be added in a sequence to produce the desired multi-material object. Our algorithm starts with the final object assembly and considers removing components either completely or partially from the object one-at-a-time such that it results in the previous state of the object assembly. If a component can be removed from the target object leaving the previous state of the object assembly a connected solid then we consider such decomposition a valid step in the stage sequence. This step is recursively repeated on new states of the object assembly until the object assembly reaches a state where it only consists of one component. When an object-decomposition has been found that leads to a feasible stage sequence, the gross mold for each stage is computed and decomposed into two or more pieces to facilitate the molding operation. We expect that our algorithm will provide a step towards automating the design of multi-stage molds and therefore will help in reducing the mold design lead-time for multi-stage molds.
Buckling of Laminated Composite Rectangular Plates Under Transient Thermal Loading
Authors: Shukla K. K. , Nath Y.
Published: October 2002

This paper deals with the nonlinear dynamic buckling of laminated composite rectangular plates subjected to uniform time-dependent in-plane temperature-induced loading. The dynamic post-buckling deflection response is obtained and dynamic critical temperatures are estimated. The nonlinear governing equations of motion are solved analytically using fast Chebyshev series technique. The numerical results for CCCC, CCCS, CCSS, CSCS, CSSS and SSSS boundary conditions are presented.
A Stability Result With Application to Nonlinear Regulation1
Authors: Langson Wilbur , Alleyne Andrew
Published: October 2002

This work considers a class of nonlinear systems whose feedback controller is generated via the solution of a State Dependent Riccati Equation (SDRE) as proposed in Banks and Manha and Cloutier. A pseudo-linear representation of the class of nonlinear systems is described and a stability analysis is performed. This analysis leads to sufficiency conditions under which local asymptotic stability is present. These conditions allow for the computation of a Region of Attraction estimate for system stability. These results are then applied to study stability and convergence properties of closed loop systems that arise when the SDRE technique is used. Many of the benefits of Linear Quadratic (LQ) Optimal Control, such as a tradeoff between state regulation and input effort, are readily transparent in the nonlinear scheme. The tradeoff ability is the major advantage of the SDRE over several other nonlinear control schemes. The computed Region of Attraction, while sufficient, is demonstrated to also be quite conservative. An example is used to examine the SDRE approach.
Influence of Clearance Between Plates in Metal Pushing V-Belt Dynamics
Authors: Carbone G. , Mangialardi L. , Mantriota G.
Published: October 2002

This paper proposes a one-dimensional continuous model of the steel pushing V-belt, which describes the shifting dynamics of the CVT transmission during rapid speed ratio variations. The model investigates the influence of the clearance among the steel segments on the belt dynamics. The plates and pulleys strain motion is neglected, with respect to their rigid body motion, for the evaluation of the friction forces. The power transmission is assured only if an active arc exists where the plates are pressed against each other and where compressive forces arise among the steel segments. Conversely on the idle arc the steel plates are separated and no longitudinal compressive forces exist among the metal segments. The paper shows a significant difference in dynamical behavior between the drive and the driven pulley. Moreover, differences also exist between the pitch radius increasing phases and pitch radius decreasing phases.
A Method for Pressure Calculation in Ball Valves Containing Bubbles
Authors: van Lookeren Campagne C. , Nicodemus R. , de Bruin G. J. , Lohse D.
Published: October 2002

A method of analyzing bubbly flow in a ball valve in a hydraulic circuit is presented. The dynamics of a single bubble can be well described by a quasi-static approximation of the Rayleigh-Plesset equation. Hence the presence of bubbles in low volume fractions can be modeled through an effective compressibility of the flow, which is easy to implement in commercial CFD packages. In the sample valve, a volume fraction of 4% air bubbles results in a mass flux reduction of up to 10%, as the bubbles expand due to the pressure drop in the valve and partly block it.
Analysis and Experiments on Three-Dimensional, Irregular Surface Roughness
Authors: van Rij J. A. , Belnap B. J. , Ligrani P. M.
Published: October 2002

Randomly placed, nonuniform, three-dimensional roughness with irregular geometry and arrangement is analyzed. New correlations are presented for such roughness for determination of magnitudes of equivalent sand grain roughness size ks from a modified version of the Sigal and Danberg parameter Λs. Also described are the numerical procedures employed to determine Λs from three-dimensional profilometry data. The sand grain roughness values determined with this approach are then compared with and verified byks magnitudes determined using: (i) analytic geometry for uniformly shaped roughness elements arranged in a regular pattern on a test surface, and (ii) measurements made with nonuniform, three-dimensional, irregular roughness with irregular geometry and arrangement. The experiments to obtain these measurements are conducted using this latter type of roughness placed on the walls of a two-dimensional channel. Skin friction coefficients are measured in this channel with three different types of rough surfaces on the top and bottom walls, and agree very well with values determined using the numerical procedures and existing correlations. The techniques described are valuable because they enable the determination of equivalent sand grain roughness magnitudes, for similar three-dimensional roughness, entirely from surface geometry after it is characterized by three-dimensional optical profilometry data.
Mathematical Basis and Validation of the Full Cavitation Model
Authors: Singhal Ashok K. , Athavale Mahesh M. , Li Huiying , Jiang Yu
Published: October 2002

Cavitating flows entail phase change and hence very large and steep density variations in the low pressure regions. These are also very sensitive to: (a) the formation and transport of vapor bubbles, (b) the turbulent fluctuations of pressure and velocity, and (c) the magnitude of noncondensible gases, which are dissolved or ingested in the operating liquid. The presented cavitation model accounts for all these first-order effects, and thus is named as the “full cavitation model.” The phase-change rate expressions are derived from a reduced form of Rayleigh-Plesset equation for bubble dynamics. These rates depend upon local flow conditions (pressure, velocities, turbulence) as well as fluid properties (saturation pressure, densities, and surface tension). The rate expressions employ two empirical constants, which have been calibrated with experimental data covering a very wide range of flow conditions, and do not require adjustments for different problems. The model has been implemented in an advanced, commercial, general-purpose CFD code, CFD-ACE+. Final validation results are presented for flows over hydrofoils, submerged cylindrical bodies, and sharp-edged orifices. Suggestions for possible extensions of the model implementation, e.g., to nonisothermal flows, for ingestion and mixing of noncondensible gases, and for predictions of noise and surface damage are outlined.
Effect of Radial Clearance on the Flow Between Corotating Disks in Fixed Cylindrical Enclosures
Authors: Al-Shannag Mohammad , Herrero Joan , Humphrey Joseph A. C. , Giralt Francesc
Published: October 2002

Numerical results are obtained for the isothermal laminar flow of air between a pair of disks attached to and rotating with a hub in a fixed cylindrical enclosure. The presence of radial clearances or “gaps” between the rims of the disks and the curved enclosure wall, and the finite thickness of the disks, are considered in the calculations. The gaps allow time- and circumferentially-dependent axially-directed air flow exchanges between the contiguous inter-disk spaces. As a consequence, axisymmetric calculations of the flow, whether using boundary conditions in the gaps or extended to include the entire flow domain, fail to faithfully reproduce the experimentally measured radial variations of the mean and rms circumferential velocity components in the inter-disk space. Likewise, three-dimensional calculations using the symmetry-plane boundary condition in the gaps also fail to reproduce these variations. In contrast, computationally intensive three-dimensional calculations of the entire flow domain, including the gaps, yield results in very good agreement with the measured mean and rms velocities. These three-dimensional calculations reveal large velocity fluctuations in the gap regions accompanied by corresponding large fluctuations of the inter-disk flow, reflecting a destabilization of the structure and dynamics of the latter by the former. The axisymmetric calculations as well as those using the symmetry-plane condition in the gap are included in this study principally to elucidate their shortcomings in simulating the three-dimensional flows considered; they are not the main goal of the study. Notwithstanding, the physically approximate, full domain axisymmetric calculations yield useful qualitative results. They show that increasing gap size decreases disk surface shear and the associated disk torque coefficient, but at the cost of destabilizing the inter-disk flow. This observation is in agreement with earlier findings and is better understood as the result of the present study.
A Study of Vortex Shedding in a Staggered Tube Array for Steady and Pulsating Cross-Flow
Authors: Konstantinidis E. , Balabani S. , Yianneskis M.
Published: October 2002

This paper describes an experimental investigation of the vortex shedding phenomena in a staggered tube array with streamwise and transverse spacing to diameter ratios of 2.1 and 3.6, respectively. LDA measurements were employed to monitor the flow fluctuations and a visualization technique was implemented to reveal the underlying flow patterns in the array for steady and pulsating cross-flow. The results obtained in steady flow are in general agreement with results from previous investigations and show that vortex shedding occurs at two distinct frequencies in the front and inner rows. A lower frequency component was detected at the exit of the array, which has not been previously identified. Pulsating flow caused the frequency of vortex shedding to lock-on at the subharmonic of the imposed frequency. In the lock-on range, vortex shedding from all the tubes was synchronized and in-phase and velocity fluctuations at the shedding frequency increased considerably compared to their counterparts in steady flow.
Concentrated Solar Energy as a Diagnostic Tool to Study Materials Under Extreme Conditions
Authors: Balat-Pichelin M. , Hernandez D. , Olalde G. , Rivoire B. , Robert J. F.
Published: October 2002

This paper deals with the material testing under extreme conditions, mainly around space programs, using the French CNRS (Centre National de la Recherche Scientifique) solar facilities for planetary entry (Earth, Mars), solar corona in situ exploration, and cryogenic propulsion. For these purposes, different facilities were developed around the various solar concentrators: MESOX (Moyen d’Essai Solaire d’OXydation), for the study of the atomic oxygen recombination at the surface of heated materials and the oxidation kinetics of ceramics under plasma atmospheres up to 2300 K. (Some results are given for several materials.); MEDIASE (Moyen d’Essai et de DIagnostic en Ambiance Spatiale Extre^me), for the thermophysical characterization of thermal shield materials up to 2400°K under high vacuum: mass-loss kinetics, mass spectrometry (neutral and ionic species) and thermo-radiative properties (total or spectral directional emissivity). (Results are presented for various carbon/carbon composite materials.); and DISCO (DISpositif de Caracte´risation Optique), for the measurement of changes in the reflectivity of materials at temperatures up to 2500°K and its correlation with the surface behavior (aging, ablation and oxidation). Results concerning a copper alloy used for the combustion chamber of cryogenic motors are given.
Predicting the Failure Response of Cement-Bone Constructs Using a
Non-Linear Fracture Mechanics Approach
Authors: Mann Kenneth A. , Damron Leatha A.
Published: October 2002

A non-linear fracture mechanics approach was used to predict the failure response of complex cement-bone constructs. A series of eight mechanical tests with a combination of tensile and shear loading along the cement-bone interface was performed. Each experiment was modeled using the finite element method with non-linear constitutive models at the cement-bone interface. Interface constitutive parameters were assigned based on the quantity of bone interdigitated with the cement. There was a strong correlation r2=0.80 between experimentally measured and finite element predicted ultimate loads. The average error in predicted ultimate load was 23.9 percent. In comparison to the ultimate load predictions, correlations and errors for total energy to failure (r2=0.24, avg. error=38.2 percent) and displacement at 50 percent of the ultimate load (r2=0.27, avg. error=52.2 percent) were poor. The results indicate that the non-linear constitutive laws could be useful in predicting the initiation and progression of interface failure of cemented bone-implant systems. However, improvements in the estimation of post-yield interface properties from the quantity of bone interdigitated with cement are needed to enhance predictions of the overall failure response.
Parametric Sensitivity Analysis of a Test Cell Thermal Model Using Spectral Analysis
Authors: Mara Thierry Alex , Boyer Harry , Garde Franc¸ois
Published: October 2002

This paper deals with a method of performing a parametric sensitivity analysis. Such a study is very important for modellers as it can provide useful information. Indeed, it can point out a model’s weaknesses and allow us to identify the most important parameters in the model, which the modeller must know accurately to provide reliable results. After describing the approach, an application of the method in building thermal simulation is discussed. The study concerns a real test cell and gives coherent results as some of the most influential factors can be physically interpreted.
Heat Transfer Enhancement Study of a LHTS Unit Containing Dispersed High Conductivity Particles
Authors: Seeniraj R. V. , Velraj R. , Lakshmi Narasimhan N.
Published: October 2002

A theoretical analysis is presented for the performance study of a Latent Heat Thermal Storage (LHTS) system that contains a phase change material (PCM) dispersed with high conductivity particles. The effect of fraction of dispersed particles in the PCM on energy storage time and heat flux is presented for laminar and turbulent flows, and also analytical expressions are presented for various quantities of interest to study the energy storage capabilities. The combined effect of thermal and flow properties of both the heat transfer fluid (HTF) and the PCM-mixture is also included in the study. It is observed that there exists an optimum fraction of particles to be dispersed in the PCM for maximum energy storage/extraction.
A Study of Ice Accretion Shape on Cables Under Freezing Rain Conditions
Authors: Szilder Krzysztof , Lozowski Edward P. , Reuter Gerhard
Published: October 2002

The influence of atmospheric conditions (specifically precipitation rate and external heat flux) on the freezing rain ice accretion forming on a non-rotating, horizontal cylinder is studied, using an analytical model based on a simple form of the equations for conservation of mass and heat balance. In keeping with the freezing rain application, but in order to simplify this first step, we have assumed vertical incidence of precipitation (no wind) and no dripping from the accretion (hence light to moderate precipitation rates with relatively low air temperatures). The initial ice accretion shape and the location of its center of mass are examined as a function of the ratio of the precipitation mass flux to the total heat flux lost from the ice surface. An increase in the flux ratio leads to a quantifiable downward displacement of the accretion center of mass. We complement this analysis with numerical simulations, using an improved, two-dimensional version of the Szilder-Lozowski morphogenetic model that predicts the evolution of the accretion shape. For the first time, the freezing probability, which is the critical model parameter, is expressed as a function of location and atmospheric conditions for an accretion shape evolving with time. Using the morphogenetic model, we examine the influence of atmospheric conditions on the accretion shape and ice load. In particular, we address the question of what gives rise to extreme ice loads by identifying the range of atmospheric conditions that tends to maximize (or minimize) the ice load for a given amount of precipitation. The results of this research are applicable to predicting ice formation on overhead transmission lines.
Predicting Globe Control Valve Performance—Part II: Experimental Verification
Authors: Davis James A. , Stewart Mike
Published: October 2002

An experimental study was undertaken to verify an axisymmetric numerical model of a control valve flow field. The numerical model, which utilized Computational Fluid Dynamics (CFD), was formerly developed to be used as a design tool by manufacturers of control valves. In this work the model was first tested by comparing its results to data taken on an axisymmetric flow field experiment. Then the model’s application to actual three-dimensional control valves was tested by studying the pressure and flow field through a three-dimensional control valve. The results showed that the axisymmetric numerical model is accurately modeling an axisymmetric flow field. In addition, the results showed that control valves have a predominantly axisymmetric flow field for most of their plug travel which make them suitable for the model. Finally, the results showed details about the flow field such as where separation and reattachment may occur.
A Comparison of Second-Moment Closure Models in the Prediction of Vortex Shedding From a Square Cylinder Near a Wall
Authors: Straatman Anthony G. , Martinuzzi Robert J.
Published: October 2002

A computational study is presented that examines the capability of various second-moment closure models in the prediction of two-dimensional, nonstationary flow around a square cylinder in proximity to a wall. The linear return-to-isotropy/isotropization-of-production model RTI+IP and the nonlinear SSG pressure-strain models were combined with the DH and modified LUM diffusion models in the computations. In terms of global activity, the drag is well-predicted in terms of both magnitude and variation with cylinder-to-wall gap width S/D. The Strouhal number St was reasonably well-predicted in terms of magnitude, but the predicted trend with decreasing S/D was incorrect for all model combinations. The lift was not well-predicted in terms of magnitude or trend. Prediction of the detailed flow structure in the vicinity of the cylinder and in the wake was favourable, though the magnitudes of some velocity and Reynolds-stress components were over-predicted. It was argued that the large differences between the results at the intermediate gap width may be due to the difference between the measured and predicted critical gap widths. On the basis of the predicted global and detailed activity, the modified LUM model combined with the nonlinear SSG model was suggested as being the most viable combination for future studies.
Continuous Wavelet Transforms of Instantaneous Wall Pressure in Slug and Churn Upward Gas-Liquid Flow
Authors: McClusky Heather L. , Holloway Mary V. , Beasley Donald E. , Ochterbeck Jay M.
Published: October 2002

Continuous wavelet transforms are employed to determine the time-localized frequency content (scalogram) of instantaneous wall pressure signals in upward gas-liquid flow. The flow conditions correspond to well-defined slug flow, well-defined churn flow, and flows near the transition from slug-to-churn flow. Scalograms demonstrate that the frequency content of the pressure signals is time-dependent, and visual observations of the flow conditions suggest that the time-dependent frequencies are related to identifiable physical behaviors of the flow. In well-defined slug flow, the scalograms are characterized by the presence of a dominant frequency throughout the duration of the signal and by frequency shifting events. Scalograms representing well-defined churn flow contain intermittent frequencies, and the energy density in churn flow is spread over a wider range of frequencies than in slug flow. The present results provide evidence that flows near transition alternately display characteristics of both well-defined slug and well-defined churn flows.
Does the Minimum Fluidization Exist?
Authors: Delebarre Arnaud
Published: October 2002

This work proposes an equation giving the pressure drop of a gas flowing through a porous medium or a granular bed. The consequences for the onset of the fluidization are then discussed. It appears that the notion of minimum gas mass-flow rate would improve the description of the transition between fixed and fluidized bed regimes. An equation is then proposed to calculate the minimum fluidization gas mass-flow rate. It is then proved that the minimum fluidization is not only a function of the medium and fluid characteristics but also that it increases with bed inventory. It is then shown that a batch of particles has a minimum fluidization depending on its arrangement in a column and that in some cases, this minimum does not exist at all. As a consequence, the minimum of fluidization, whether it is a velocity or a mass flow rate, cannot be considered as a criterion to characterize a powder.
Some Recent Studies on Plastic Behavior of Plates Subjected to Large Impact Loads
Authors: Wang Ge
Published: October 2002

This paper reviews some recent studies on the plastic behavior of steel plates subjected to large impact loads. This is an important topic for risk assessments and safety evaluations because of the ever heightened public concern about safety of marine structures and potential harm to the environment due to marine accidents. Emphasis is given to the complex plastic deformation patterns recently identified, including plate punching, plate tearing, and local denting of web girders. Descriptions are given of the complex interactions of the many mechanisms involved in these deformation patterns, including membrane stretching, local plastic bending, complex object geometry, rupture, cracking and friction. Advanced analytical formulas that can be used to describe these behavior mechanisms are introduced. These formulas are based on the advanced structural crashworthiness methodology.
EMAT-Based Inspection of Concrete-Filled Steel Pipes for Internal Voids and Inclusions
Authors: Na Won-Bae , Kundu Tribikram
Published: October 2002

Concrete-filled steel pipes have been used as piles for supporting civil and marine structures. These piles provide good bending resistance, and can be easily spliced for long depth installation. However, these piles are usually exposed in hostile environments such as seawater and deicing materials. Thus, the outside corrosion of the steel pipe can reduce the wall thickness and the corrosion-induced delamination of internal concrete can increase internal volume or pressure. In addition, the void that can possibly exist in the pipe reduces the bending resistance. To avoid structural failure due to this type of deterioration, appropriate inspection and repair techniques are to be developed. The acoustic method is attractive for this inspection since it is relatively simple and versatile. Especially, guided wave techniques have strong potentials for this inspection because of long-distance inspection capability. There are different transducer-coupling mechanisms available for the guided wave inspection techniques. Electro-magnetic acoustic transducers (EMATs) give relatively consistent results in comparison to piezoelectric transducers since they do not need any couplant. EMATs are used for transmitting and receiving cylindrical guided waves through concrete-filled steel pipes. It is shown that EMAT-generated cylindrical guided wave techniques have good potential for the interface inspection of concrete-filled steel pipes.
Risk Assessment Tools for Use During Fabrication of Offshore Structures and in Marine Operations Projects
Authors: Gudmestad Ove Tobias
Published: October 2002

The trend towards most offshore field developments occurring in deep waters has increased the dependency on marine operations in the offshore industry. The installation of sub sea templates as well as offshore floating units year round is profitable from a net present value point of view, but the risks involved to the owners are increasing when working off-season in bad weather. This calls for analysis of the risk and identification of efficient risk-reducing measures. In this paper, the effect of setting proper weather criteria for marine operations and reducing the uncertainty in the weather forecast is highlighted. During the latest years, severe losses have been reported as caused by failures during marine operations. The need for risk analysis of marine operations is therefore underlined. This calls for an overview of the tools available to analyze risks during marine operations. In this paper, some different assessment tools are reviewed, and recommendations are given as to the appropriateness of using these tools. Both qualitative and quantitative tools are discussed with a general recommendation of employing the more sophisticated tools when the consequences are large. Qualitative analysis should normally be carried out before any quantitative analysis.
The Effect of the Operating Point on the Pressure Fluctuations at the Blade Passage Frequency in the Volute of a Centrifugal Pump
Authors: Parrondo-Gayo Jorge L. , Gonza´lez-Pe´rez Jose´ , Ferna´ndez-Francos Joaquı´n
Published: October 2002

An experimental investigation is presented which analyzes the unsteady pressure distribution existing in the volute of a conventional centrifugal pump with a nondimensional specific speed of 0.48, for flow-rates from 0% to 160% of the best-efficiency point. For that purpose, pressure signals were obtained at 36 different locations along the volute casing by means of fast-response pressure transducers. Particular attention was paid to the pressure fluctuations at the blade passage frequency, regarding both amplitude and phase delay relative to the motion of the blades. Also, the experimental data obtained was used to adjust the parameters of a simple acoustic model for the volute of the pump. The results clearly show the leading role played by the tongue in the impeller-volute interaction and the strong increase in the magnitude of dynamic forces and dipole-like sound generation in off-design conditions.
Defects at the interface of (100)Si with ultrathin layers of SiOx, Al2O3, and ZrO2 probed by electron spin resonance
Authors: Stesmans A. , Afanas’ev V. V.
Published: October 2002

An electron spin resonance study has been carried out on (100)Si/SiOx/ZrO2 and (100)Si/Al2O3/ZrO2 stacks with nm-thin dielectric layers grown by the atomic layer chemical vapor deposition method at 300 °C. This reveals the Si dangling bond type centers Pb0, Pb1 as prominent defects at the (100)Si/dielectric interface in both types of structures. While reassuring for the Si/SiOx/ZrO2 case, this Pb0, Pb1 fingerprint, archetypal for the thermal (100)Si/SiO2 interface, indicates that the as-deposited (100)Si/Al2O3 interface is basically (100)Si/SiO2-like. Yet, as exposed by the salient spectroscopic properties of the Pb0, Pb1 defects, the interfaces are found to be in an enhanced (less relaxed) stress state, generally characteristic of low-temperature Si/SiO2 fabrication. The thermal behavior has been addressed by subjecting the sample stacks to heat treatments in vacuum or O2 ambient. Based on the Pb0, Pb1 criterion, it is found that standard thermal Si/SiO2 interface properties may be approached by appropriate annealing (⩾650 °C) in vacuum in the case of Si/SiOx/ZrO2. Yet, O2 ambient is required for Si/Al2O3, indicating that the initial interface is too abrupt to enable thermal interfacial rearrangement without growth of an additional SiOx interlayer. A minimal SiOx interlayer thickness (0.5 nm) appears requisite. Thus, Si/high-κ metal oxide structures may be endowed with device quality interfaces with sub-nm thin SiOx interlayer, which may support the applicability of high-κ metal oxides. Obviously, though, the (inherent) occurrence of an SiOx interlayer will impair the minimal equivalent SiO2 thickness that may ultimately be realized with an envisioned high-κ material.
Comparison of two different Ti/Al/Ti/Au ohmic metallization schemes for AlGaN/GaN
Authors: Bardwell J. A. , Sproule G. I. , Liu Y. , Tang H. , Webb J. B. , Fraser J. , Marshall P.
Published: October 2002

Two different ohmic metallization schemes for AlGaN/GaN heterostructure field-effect transistor structures are investigated. Each consists of Ti/Al/Ti/Au layers, with the Ti contacting the AlGaN surface, and they differ only in the relative thicknesses of Ti and Al. The “Cornell” metallization consists of 20/100/45/55 nm thicknesses, respectively, while the “NRC” metallization consists of 30/80/120/55 nm thicknesses for the layers. Thus, the Cornell scheme is much richer in Al. The two schemes were compared on the same AlGaN/GaN growth wafer which, because of nonuniformity, provides a variety of contact resistances in the final annealed devices. The Cornell scheme formed good quality ohmic contacts at short anneal times, but clearly contained excess, unalloyed Al, as it showed visible, gas-evolving corrosion in a cleaning solution consisting of 1:1 HCl:H2O. The surface morphology was rough and the edge acuity was relatively poor. Auger depth profiling showed a single, almost uniformly mixed layer. The NRC scheme required a longer anneal time, and the contact resistance remained high for larger grained AlGaN/GaN material. It was stable in the HCl:H2O cleaning solution, and exhibited good edge acuity and a smooth surface morphology. Auger electron depth profiling of the NRC scheme showed two layers present in the annealed metal. The Auger results are consistent with transmission electron microscope results presented elsewhere. The results suggest that the Cornell scheme would be the choice for materials that are more difficult to contact.
Ferromagnetism in (In,Mn)As diluted magnetic semiconductor thin films grown by metalorganic vapor phase epitaxy
Authors: Blattner A. J. , Wessels B. W.
Published: October 2002

In 1−x Mn x As diluted magnetic semiconductor thin films have been grown using metalorganic vapor phase epitaxy. Tricarbonyl(methylcyclopentadienyl)manganese was used as the Mn source. Nominally single-phase, epitaxial films were achieved with Mn content as high as x=0.14 using growth temperatures Tg⩾475 °C. For lower growth temperatures and higher Mn concentrations, nanometer scale MnAs precipitates were detected within the In1−xMnxAs matrix. Magnetic properties of the films were investigated using a superconducting quantum interference device magnetometer. Room-temperature ferromagnetic order was observed in a sample with x=0.1. Magnetization measurements indicated a Curie temperature of 333 K and a room-temperature saturation magnetization of 49 emu/cm3. The remnant magnetization and the coercive field were small, with values of 10 emu/cm3 and 400 Oe, respectively. A mechanism for this high-temperature ferromagnetism is discussed in light of the recent theory based on the formation of small clusters of a few magnetic atoms.
Formation of Ag nanometer particles at the interface of Ag thin film and poly(ethylene terephthalate) substrate under visible light irradiation
Authors: Fukuda S. , Kawamoto S. , Gotoh Y. , Nozaki S. , Nakaura M.
Published: October 2002

We investigated the formation of Ag nanoparticles at the interface of an Ag thin film with a polyethylene terephthalate (PET) substrate under intense visible light irradiation at elevated temperatures. Using dc magnetron sputtering, Ag thin films were prepared on a PET substrate at room temperature. The interface was exposed to visible light from a Xe lamp with an intensity of 500 mW/cm2 through the PET substrate. Cross-sectional views of the interface were observed with the use of a transmission electron microscope before and after the irradiation. In order to avoid the deterioration of the PET substrate itself, the component of the ultraviolet (UV) light was excluded by placing a UV-cut filter between the light source and the specimen. The total reflectance was measured with a spectrophotometer equipped with an integrating sphere. The reflectance of the Ag film through the PET was found to decrease due to the formation of Ag nanoparticles at the interface after the visible light irradiation. Deposition of a few monolayers of metals such as Ti and W on PET before the deposition of Ag was quite effective in retarding the formation of the Ag nanoparticles and in maintaining the high reflectance of the Ag thin film. With the increase in the intensity of the light and the rise of the temperature, the decrease in the reflectance was accelerated. By fitting the curves of the decrease in the reflectance at different temperatures to a stretched exponential function, an apparent activation energy of the reaction corresponding to the decrease of the reflectance was estimated as 50 kJ/mol. We will also report the light intensity dependence of the decrease in reflectance.
Eliminating dielectric degradation of low-k organosilicate glass by trimethylchlorosilane treatment
Authors: Chang T. C. , Liu P. T. , Mor Y. S. , Tsai T. M. , Chen C. W. , Mei Y. J. , Pan F. M. , Wu W. F. , Sze S. M.
Published: October 2002

The interaction between low-k organosilicate glass (OSG) and photoresist removal is investigated. O2 plasma ashing and chemical wet stripper are commonly performed to remove photoresist (PR) in integrated circuit fabrication. However, O2 plasma or wet stripper will attack function groups and cause Si–OH group formation in OSG film during PR removal processing. The Si–OH groups often lead to moisture uptake and consequently dielectric degradation will occur in OSG film. Trimethylchlorosilane (TMCS) treatment can negate the damage in the OSG film after the PR removal process. In addition, chemical TMCS can react with Si–OH groups and reduces moisture uptake so that the dielectric characteristic of OSG can be maintained. Hence, TMCS treatment is a promising method for photoresist removal.
A calibration approach to glandular tissue composition estimation in digital mammography
Authors: Kaufhold J. , Thomas J. A. , Eberhard J. W. , Galbo C. E. , Trotter D. E. González
Published: October 2002

The healthy breast is almost entirely composed of a mixture of fatty, epithelial, and stromal tissues which can be grouped into two distinctly attenuating tissue types: fatty and glandular. Further, the amount of glandular tissue is linked to breast cancer risk, so an objective quantitative analysis of glandular tissue can aid in risk estimation. Highnam and Brady have measured glandular tissue composition objectively. However, they argue that their work should only be used for “relative” tissue measurements unless a careful calibration has been performed. In this work, we perform such a “careful calibration” on a digital mammography system and use it to estimate breast tissue composition of patient breasts. We imaged 0%, 50%, and 100% glandular‐equivalent phantoms of varying thicknesses for a number of clinically relevant x‐ray techniques on a digital mammography system. From these images, we extracted mean signal and noise levels and computed calibration curves that can be used for quantitative tissue composition estimation. In this way, we calculate the percent glandular composition of a patient breast on a pixelwise basis. This tissue composition estimation method was applied to 23 digital mammograms. We estimated the quantitative impact of different error sources on the estimates of tissue composition. These error sources include compressed breast height estimation error, residual scattered radiation, quantum noise, and beam hardening. Errors in the compressed breast height estimate contribute the most error in tissue composition—on the order of ±7% for a 4 cm compressed breast height. The spatially varying scattered radiation will contribute quantitatively less error overall, but may be significant in regions near the skinline. It is calculated that for a 4 cm compressed breast height, a residual scatter signal error is mitigated by approximately sixfold in the composition estimate. The error in composition due to the quantum noise, which is the limiting noise source in the system, is shown to be less than 1% glandular for most breasts.
Empirical description and Monte Carlo simulation of fast neutron pencil beams as basis of a treatment planning system
Authors: Bourhis‐Martin E. , Meissner P. , Rassow J. , Baumhoer W. , Schmidt R. , Sauerwein W.
Published: October 2002

The fast neutron beam, used for fast neutron therapy in Essen, is produced by the nuclear reaction of a 14 MeV cyclotron—based deuteron beam on a thick beryllium target. The resulting neutron beam has a continuous energy spectrum with a mean and a maximum energy equal to 5.5 and 18 MeV, respectively. The dose delivered to the patient is computed by a treatment planning system (TPS) based on an empirical model, in which the dose components (neutron and photon) are described by analytical functions. In order to improve the dose calculation, and thus to use the fast neutron beam for other applications (e.g., Boron Neutron Capture Enhancement of Fast Neutron Therapy), in this work we aim to develop a new TPS. For this purpose, a model based on pencil beams of mono‐energetic neutrons has been created. The neutron energy ranged from 0.25 MeV up to 17.25 MeV by steps of 0.5 MeV in order to cover the energy range of the Essen facility. The Monte Carlo method was then used to simulate the transport of neutrons within such pencil beams in a homogeneous water phantom. By using Monte Carlo techniques, it is possible to distinguish the energy deposition due to a primary collision in water to that due to scattered neutrons. The energy deposition due to pencil beams of 2.224 MeV photons, coming from hydrogen neutron capture reaction in the phantom or in the collimator, was also determined. In order to complete this work, air filled cylinders have been introduced in the water phantom. It is shown that the resulting depth dose curves for primary neutrons can be easily derived using the homogeneous phantom, and that the description of the effect on scattered neutron dose distribution is more complex. In this work we demonstrate the relevance of Monte Carlo simulations of mono‐energetic neutron pencil beams for purposes of neutron treatment planning. Some additional work is still required to describe a clinical situation (continuous energy neutron spectrum) as well as to experimentally validate the method described here.
Evaluation of Kodak EDR2 film for dose verification of intensity modulated radiation therapy delivered by a static multileaf collimator
Authors: Zhu X. R. , Jursinic P. A. , Grimm D. F. , Lopez F. , Rownd J. J. , Gillin M. T.
Published: October 2002

A new type of radiographic film, Kodak EDR2 film, was evaluated for dose verification of intensity modulated radiation therapy (IMRT) delivered by a static multileaf collimator (SMLC). A sensitometric curve of EDR2 film irradiated by a 6 MV x‐ray beam was compared with that of Kodak X‐OMAT V (XV) film. The effects of field size, depth and dose rate on the sensitometric curve were also studied. It is found that EDR2 film is much less sensitive than XV film. In high‐energy x‐ray beams, the double hit process is the dominant mechanism that renders the grains on EDR2 films developable. As a result, in the dose range that is commonly used for film dosimetry for IMRT and conventional external beam therapy, the sensitometric curves of EDR2 films cannot be approximated as a linear function, Within experimental uncertainty, the film sensitivity does not depend on the dose rate (50 vs 300 MU/min) or dose per pulse (from to Field sizes and depths (up to field size of 10×10 cm2 and depth=10 cm) have little effect on the sensitometric curves. Percent depth doses (PDDs) for both 6 and 23 MV x rays were measured with both EDR2 and XV films and compared with ion chamber data. Film data are within 2.5% of the ion chamber results. Dose profiles measured with EDR2 film are consistent with those measured with an ion chamber. Examples of measured IMRT isodose distributions versus calculated isodoses are presented. We have used EDR2 films for verification of all IMRT patients treated by SMLC in our clinic. In most cases, with EDR2 film, actual clinical daily fraction doses can be used for verification of composite isodose distributions of SMLC‐based IMRT.